Article: 93560 of rec.radio.amateur.homebrew From: "Tom Holden" References: Subject: Re: Ham radio beginner? Message-ID: Date: Thu, 7 Jul 2005 16:22:55 -0400 An absolutely phenomenal mutual help group is at http://groups.yahoo.com/group/HamRadioHelpGroup/. Its focus is primarily for US licensees or wannabe's but the technical help is universal. Tom Article: 93561 of rec.radio.amateur.homebrew From: Just Cuz Subject: Why don't many high power RF transistor amplifiers use emitter stabilizing resistor and AC by-pass capacitors? Message-ID: Date: Fri, 08 Jul 2005 02:03:51 GMT I have been looking at a variety of RF transistor amplifier schematics including a 50 watt amp shown in the ARRL handbook (1996 - page 17.96) , and they do not have emitter stabilizing resistors and ac by-pass capacitors on the emitter leg of the final output transistors. Is there a good reason for not using emitter stabilizing resistors and ac by-pass capacitors in 100 watt output or more RF transistor amplifiers? Here are some on-line schematics I found of high power RF power transistor amplifiers, and in all of them the emitter goes straight to ground. http://www.ameritron.com/man/pdf/ALS-500M.pdf http://www.cbtricks.com/Amp/txstar/250hdv_350hdv/graphics/ts_dx250hdv_dx350hdv_sch.gif http://www.cbtricks.com/Amp/palomar/elite/palomar_elite500.pdf Article: 93562 of rec.radio.amateur.homebrew From: Bob Liesenfeld Subject: Re: Why don't many high power RF transistor amplifiers use emitter Date: Thu, 07 Jul 2005 21:12:52 -0500 Message-ID: <42CDE124.B70118B2@visi.com> References: Just Cuz wrote: > Is there a good reason for not using emitter stabilizing > resistors and ac by-pass capacitors in 100 watt output or more RF > transistor amplifiers? My hunch would be that most of those amps probably use ballasted emitter transistors which mitagates the need for an emitter resistor. That, plus the fact that any impedance in the emitter lead is an invitation to oscillation, and obtaining a good low Z bypass is tough at HF especially at the current levels involved. Bob WB0POQ Article: 93563 of rec.radio.amateur.homebrew From: Ken Scharf Subject: Re: Looking for 12V tube Rx project info References: <1119556572.530653.109680@f14g2000cwb.googlegroups.com> <3Rkve.6758$Bm.4442@bignews5.bellsouth.net> <1119748538.259718.166300@f14g2000cwb.googlegroups.com> <1119913230.190263.47320@g49g2000cwa.googlegroups.com> Message-ID: Date: Thu, 07 Jul 2005 22:19:11 -0400 LenAnderson@ieee.org wrote: > From: Ken Scharf on Sun 26 Jun 2005 22:41 > > >>LenAnderson@ieee.org wrote: >> >>>From: Ken Scharf on Jun 25, 6:26 pm >>> >>>>LenAnder...@ieee.org wrote: >>> >>>>>>I am looking for a nice schematic, and perhaps additional info, on a 12V >>>>>>(fil. & plate) tube superhet Rx; just something fairly simple for CW/SSB >>>>>>reception without bells and whistles, and preferably for 75M/40M reception. >>>> >>>>> Setchell-Carlson managed to do it with loctal-base tubes running >>>>> off of a 24/28 VDC aircraft bus back in WW2 times. No dynamotor, >>>>> just that cute little box referred to as a "range receiver" or >>>>> BC-1206. > > >>> Converting a "Q5-er" from tubes to FETs would be rather easy. >>> No real need for the 2N2222s. Would have gobs of space left over >>> inside an already compact box. >> >>This is the idea of a cascade fet-bipolar circuit. The drain of the fet >>drives the emitter of the bipolar and the bipolar's base is biased so >>that the base sits about half way up the power supply (two resistors). >>The fet is self biased with a source resistor for the desired current. >>The gain of this circuit is higher than a fet by itself, and the output >>impedance will be higher. >> ____ __ >> ->|_ \_/ >> | | >> >> >>> If the 135 KHz IF has an equivalent total Q of 100, the BW would >>> be about 1.3 KHz, not all that swift for CW and too shart for SSB. >>> >> >> The AnArc-5 Q5'ers had 6 tuned circuits in their If but the '1206 >>only has 3 or 4. So it's BW might be a tad wider. The 1206 also has >>no bfo. > > > The ARC-5 LF version has IF TRANSFORMERS but the insides are > easy to see for detail. The 6 to 9 MHz version IFs (2830 KHz) > had only one tuned circuit in each IF can. > > Can't remember what the BC-1206 used in their IF cans, but that > is easy to change inside the present can (it will look just the > same on the outside). I seem to remember two trimmer caps so I guess there were a total of four tuned circuits. I think the ham radio article I saw on converting the rig did add a bfo using a tv horizontal coil cut down as the bfo coil. I could also remove some wire from an old BC453 bfo coil, of which I have a few in the junk box. (Not to metion about a dozen 85khz if cans). Which reminds me..... I was thinking of building a solid state version of the old Drake 2B receiver with it's 80meter first (tunable) IF, 455khz second if, and 85khz third if (using Arc5 IF transformers) instead of Drakes 50khz (close enough). I'd use a BC454 tuning cap padded down to cover 3.5-4.1mhz just like Drake. The first oscillator would be a PLL to cover everything (beats grinding on ft243 rocks). > > I can't see any advantage of going cascode (JFET-bipolar) when an > insulated gate FET would closely approximate a vacuum tube for > both input impedance (all capacitive) and drain/output impedance > (many hundreds of KOhms). Depends on what is available for the > vacuum-to-solid conversion. Junction fets are rather low gain, though compared to tubes with 28 volts on their plates, probably a good match. The cascade circuit can be built with either two jfets, or one jfet and one bipolar. The jfet/bipolar version combines the high gain of a bipolar transistor with the high input impedance of the fet. That's the reason I'd give it a try (plus I enough of BOTH kinds in the junk box). I'd replace the converter tube with three fets, two in differcial for the mixer, and one for the oscillator. > > Note: Both input and output impedances will affect the impedance > and Q of the tuned circuits...and the GAINS...for a conversion > with minimum circuit changes. All that has to be taken into > account. > > >>> However, the BC-1206 tuning range of 195 to 500 KHz results in >>> an image at the converter input of 390 to 1000 KHz away from the >>> desired band. That's worse than the 910 KHz image of an old >>> 455 KHz IF. >>> >> >>The 1206's dial only goes up to 400khz, but it tunes past that. Maybe >>it goes to 420 or 450khz, I don't think it goes as high as 500khz. >>(so maybe I don't have to expand the range for my needs). > > > The variable tuning capacitor max:min ratio is roughly 11:1 (no > external parallel capacity). Since the resonant tuning range is > the square root of that, you could have it tune 190 to 570 KHz > with a 9:1 max:min change in resonance capacity. The only real > problem is getting the variable LO tuning to track the front end > since it would tune 325 to 705 KHz (for the high-side) and that > would be a 2.169:1 frequency ratio or 4.706 capacity change ratio. > Well that doesn't take into account the distributed capacitance of the coil windings, which would be considerable at this frequency what with the required inductance. (ever wonder why a grid dipper covers a much higher min-max frequency ratio as the frequency band goes up?) Also IIRC there are trimmer caps in parallel with the tuning caps for alignment as the coils are fixed. To make the oscillator track, a series padder cap is used to reduce the max. capacitance value of the oscillator section. -OR- a parallel padder could be used to swamp out the range of the section. > > >>> The linear-in-capacity rotation of the 3-gang variable is good >>> for an RX Noise Bridge having an expanded parallel-C range... >>> which is what I used them for. :-) >>> >> >>True, but the rig is just to cute to canabilze. > > > Heh heh heh. I agree with you there. It probably is most dense > of any other 1940s era design using 8-pin "medium" size tubes, > including the very compact ARC-5 receivers. Not quite as dense > as the SCR-300 Walkie-Talkie (BC-1000) which stuffed 18 7-pin > "miniature" tubes, a half-dozen coil/transformer cans, and a > five-gang (!) variable capacitor into an approximate 5" x 10" > chassis. [Galvin/Motorola did real good in packaging there] > > KEEPING the tubes as-is, with the possible exception of the AF > out (28D7 ?) would yield a straight-AM receiver. ADDING a BFO > via under-chassis bipolar transistor would result in minimum > cannibalization (one extra switch on front panel)...RF and IF > could remain the same. I've forgotten the audio output circuit > of it but recall that AF output power for old aircraft was > rather high (ambient noise in old warbirds was terrible). In a > quiet land environment, the audio output needed is rarely 200 > milliWatts into a speaker, much less for headphones. The SCR-300 > walkie-talkie (headphones only) had a maximum of 3 mW audio out! > You can't get much power out of a tube at 28v on the plate. The 28D7 was up to the task being a double power pentode with the sections in parallel (why not push pull?). I wouldn't call solid state conversion canabilzing. > Hint on supply conversion: A 12.6 V "filament" transformer can > do the job for all-12 V filaments in parallel. A voltage > doubling rectifier (even a tripler if need be) will yield the > quite-low B+ for plate and screen. I once did that (long time > ago) with a single transformer and voltage tripler for B+, all > working into a set of power resistor load boxes, all in a half > hour of tack-soldering. Got 30 VDC for B+ at 115 VAC line, > less than 5% ripple. Didn't have the BC-1206 then. A critic > looking on said "that isn't a good enough test...gotta have the > 'real' load on it to 'prove' it." :-) [some folks just aren't > convinced until someone else has made a finished production > product!] > > LenAnderson@ieee.org > Article: 93564 of rec.radio.amateur.homebrew From: "Tom Holden" Subject: Synch AM Special Interest Group Started Message-ID: Date: Thu, 7 Jul 2005 22:35:33 -0400 Information on and discussion of synchronous AM demodulators is scattered widely. There are sporadic discussions on a couple of Usenet news groups but they are restricted to text messages and it's hard to find the wheat in the chaff. This new group can accommodate schematics and pictures and provides a filtered view focussed on this one subject. In time, I hope that its collected files and discussions will make a strong starting or reference point for all with an interest in Synch AM. Please join if you have ever designed or experimented with synch AM demodulators or intend to start. Visit the web site at http://groups.yahoo.com/group/Synch_AM/ to subscribe. Your designs, experiences and participation in the on-topic discussions to ensue will be welcomed. Tom Article: 93565 of rec.radio.amateur.homebrew From: Tim Wescott Subject: Re: Why don't many high power RF transistor amplifiers use emitter Date: Thu, 07 Jul 2005 19:51:36 -0700 Message-ID: <11crqhn32qa2650@corp.supernews.com> References: Just Cuz wrote: > > I have been looking at a variety of RF transistor amplifier > schematics including a 50 watt amp shown in the ARRL handbook (1996 - > page 17.96) , and they do not have emitter stabilizing resistors and > ac by-pass capacitors on the emitter leg of the final output > transistors. Is there a good reason for not using emitter stabilizing > resistors and ac by-pass capacitors in 100 watt output or more RF > transistor amplifiers? > > Here are some on-line schematics I found of high power RF power > transistor amplifiers, and in all of them the emitter goes straight to > ground. > > http://www.ameritron.com/man/pdf/ALS-500M.pdf > > http://www.cbtricks.com/Amp/txstar/250hdv_350hdv/graphics/ts_dx250hdv_dx350hdv_sch.gif > > http://www.cbtricks.com/Amp/palomar/elite/palomar_elite500.pdf > Power burnt in the emitter resistor is power that isn't going out the antenna. So it makes sense to use a fancier bias network and no emitter resistor. -- ------------------------------------------- Tim Wescott Wescott Design Services http://www.wescottdesign.com Article: 93566 of rec.radio.amateur.homebrew From: "Reg Edwards" Subject: Re: Why don't many high power RF transistor amplifiers use emitter stabilizing resistor and AC by-pass capacitors? Date: Fri, 8 Jul 2005 06:12:12 +0000 (UTC) Message-ID: References: > I have been looking at a variety of RF transistor amplifier > schematics including a 50 watt amp shown in the ARRL handbook (1996 - > page 17.96) , and they do not have emitter stabilizing resistors and > ac by-pass capacitors on the emitter leg of the final output > transistors. Is there a good reason for not using emitter stabilizing > resistors and ac by-pass capacitors in 100 watt output or more RF > transistor amplifiers? > ================================= Most RF power transistors in the 50-100 watt range already have an internal emitter resistor. It's usually less than a tenth of an ohm, perhaps only a few hundreths of an ohm. Its purpose is to prevent thermal runaway and make the device more tolerant of overload due to momentary impedance mismatches. Internal resistors have an extemely low inductance. They are NOT wirewound. They are an integral part of the transistor construction and material. The manufacturer may not mention their existence in his catalogue or data book. RF power transistors are usually multi-emitter devices - all in parallel. Each emitter has its own individual series resistor. Such low-value external resistors are not available as discrete wire-ended circuit components. Inductance would be too high at HF and an invitation to self oscillation. Don't attempt to use normal circuit components in emitter leads unless a transistor manufacturer specifically recommends them. HF and VHF power transistors are very fast fuses. They are worked very close to their maximum voltage and current ratings. ---- Reg, G4FGQ Article: 93567 of rec.radio.amateur.homebrew From: waz Subject: tektronix storage scope for sale Message-ID: Date: Fri, 08 Jul 2005 20:23:40 -0400 Tektronix 564B storage oscilliscope. Type 3A72 dual trace amp. Type 3B3 time base. Powers up. I get a signal. It is too complicated for me, (I have a heathkit). $40 Canadian. It must go by the first week of August. Pickup in Montreal Quebec or pay shipping. wazungy@sympatico.ca Article: 93568 of rec.radio.amateur.homebrew From: "Heytubeguy" Subject: FA:Tubes:6L6,6V6Y,807,12AX7,6JS6C..... Message-ID: <69Fze.1105606$w62.46417@bgtnsc05-news.ops.worldnet.att.net> Date: Sat, 09 Jul 2005 00:48:02 GMT Added a few more tubes. Have a look, tnx: http://search.ebay.com/_W0QQfgtpZ1QQfrppZ25QQsassZheytubeguy + Amphenol 2 pin Mic connector set and 5691 tubes (red base). heytubeguy Article: 93569 of rec.radio.amateur.homebrew From: "Heytubeguy" Subject: FA:5691 Red Base,2-pin mic plug + more tubes Message-ID: Date: Sat, 09 Jul 2005 00:50:47 GMT Added a few more tubes. Have a look, tnx: http://search.ebay.com/_W0QQfgtpZ1QQfrppZ25QQsassZheytubeguy + Amphenol 2 pin Mic connector set and 5691 tubes (red base). heytubeguy Article: 93570 of rec.radio.amateur.homebrew From: Jim Adney Subject: Re: tektronix storage scope for sale Date: Fri, 08 Jul 2005 23:37:54 -0500 Message-ID: References: On Fri, 08 Jul 2005 20:23:40 -0400 waz wrote: >Tektronix 564B storage oscilliscope. >Type 3A72 dual trace amp. >Type 3B3 time base. > >Powers up. I get a signal. It is too complicated for me, (I have a >heathkit). I understand that you may find it overwhelming, just because the Heath may be so simple, but the 564B is a really nice scope. It's only downfall is that it's only good to 10 MHz (and the 3A72 is only good to less than that.) With a better plugin, like the 3A1 or the 3A6 this is a really versatile scope as long as you don't need higher bandwidth (and most people don't.) Your 3B3 is a good time base. The nicest thing about the 564B is the fact that you can get lots of different plugins for it that do lots of interesting things, from 4 channels plugins to spectrum analyzers. I'd encourage you to sell the Heath, but I'm biased. There's a 564B sitting just to the right of my PC. ;-) - ----------------------------------------------- Jim Adney jadney@vwtype3.org Madison, WI 53711 USA ----------------------------------------------- Article: 93571 of rec.radio.amateur.homebrew From: "Roger Conroy" Subject: Help needed to id components Date: Sat, 9 Jul 2005 09:50:05 +0200 Message-ID: I'd like to know the specs of the variable capacitors used in the MFJ-920 VHF Dual Band Tuner. There are no visible markings on them. They have 6 fixed and 7 moving semicircular plates about 33mm in diameter - spacing between the plates is in the region of 1mm. I want to recycle into something more useful - such as a HF tuner. 73 Roger ZR3RC Article: 93572 of rec.radio.amateur.homebrew From: "Polymath" References: Subject: Re: Help needed to id components Date: Sat, 9 Jul 2005 09:17:57 +0100 Message-ID: <42cf8949$1_2@x-privat.org> 1. Capacitance Meter? Be a _REAL_ Radio Ham by making one? 2. ISTR that C = nAe/d where n is the number of facing surfaces? "Roger Conroy" wrote in message news:danviv$o5c$1@ctb-nnrp2.saix.net... > I'd like to know the specs of the variable capacitors used in the MFJ-920 > VHF Dual Band Tuner. There are no visible markings on them. They have 6 > fixed and 7 moving semicircular plates about 33mm in diameter - spacing > between the plates is in the region of 1mm. I want to recycle into > something more useful - such as a HF tuner. > > 73 > Roger ZR3RC > Article: 93573 of rec.radio.amateur.homebrew Date: Sat, 09 Jul 2005 09:48:25 -0400 From: -ex- Subject: Re: Help needed to id components References: Message-ID: <54b6f$42cfd5ab$4232bd15$14499@COQUI.NET> Roger Conroy wrote: > I'd like to know the specs of the variable capacitors used in the MFJ-920 > VHF Dual Band Tuner. There are no visible markings on them. They have 6 > fixed and 7 moving semicircular plates about 33mm in diameter - spacing > between the plates is in the region of 1mm. I want to recycle into > something more useful - such as a HF tuner. > > 73 > Roger ZR3RC > > Just guessing, of course, I'd say thats about 40pf. -Bill WX4A Article: 93574 of rec.radio.amateur.homebrew From: "sean" References: <2d5631c0.0506082158.39fb1c20@posting.google.com> Subject: Re: How to turn a radio into a time-bomb??? Date: Sat, 9 Jul 2005 23:22:26 -0400 Message-ID: <42d09367_1@newspeer2.tds.net> Dude, You Really, Really Need To Get Serious HELP! Accept the following : Then only you can choose to accept the following. Only You can choose whether or not to be an assassin. Only You can choose to not HAVE to kill. You only choose to think to kill. No one else chooses for you. You have a choice. You do not need to use a radio as a time-bomb! You only choose to think that you really need to use radio for a time bomb. So, your life as only you can choose it, means what? (rhetorical) "Winnie Oakbob" wrote in message news:2d5631c0.0506082158.39fb1c20@posting.google.com... > I'm an assassin and have to kill a mafia boss.I want to blow him up > with a radio bomb. > > What do I need ? Article: 93575 of rec.radio.amateur.homebrew From: "Polymath" References: <2d5631c0.0506082158.39fb1c20@posting.google.com> <42d09367_1@newspeer2.tds.net> Subject: Re: How to turn a radio into a time-bomb??? Date: Sun, 10 Jul 2005 10:28:35 +0100 Message-ID: <42d0ea2e_1@x-privat.org> Tell that to the cowardly murdering bastards who make up the unlawful invading forces in Afghanistan and in Iraq. "sean" wrote in message news:42d09367_1@newspeer2.tds.net... > Only You can choose to not HAVE to kill. > You only choose to think to kill. > No one else chooses for you. > You have a choice. Article: 93576 of rec.radio.amateur.homebrew From: Tim Wescott Subject: Re: How can a wire wound reisitor be non-inductive? Date: Sun, 10 Jul 2005 19:38:27 -0700 Message-ID: <11d3mst6p914f23@corp.supernews.com> References: KC4IH wrote: > I need to build a 3db pad, 50 ohm, 10 watt, to reduce the drive to my 6 > meter amp. I need 2 X 300 ohms and 1 X 18 Ohm resistors and thought it would > be an easy matter to find them with enough current rating to do the job but > can't find anything larger than 1 watt carbon (not film, which are somewhat > inductive ) resistors. I can find want is called non-inductive wire wound > resistors. I can't understand how a wire wound resistor can be > non-inductive. Could someone explain this? > > > There used to be great big resistors -- essentially carbon composition -- that were truely noninductive. I suspect they're still available. My 1988 handbook has a UHF dummy load design that features a Carborundum part number 889SP500K. With coolant it's good for more than 1500 watts, so it may be oversized for you... You can still find the occasional 2W or 5W carbon comp resistor -- if you're working at HF you can easily parallel these to get the resistance that you need. -- ------------------------------------------- Tim Wescott Wescott Design Services http://www.wescottdesign.com Article: 93577 of rec.radio.amateur.homebrew Date: Sun, 10 Jul 2005 23:33:29 -0400 From: -ex- Subject: Re: How can a wire wound reisitor be non-inductive? References: Message-ID: <7a312$42d1e88c$4232bdf0$6132@COQUI.NET> KC4IH wrote: > Thanks Ralph, that is what I was thinking but when they are advertised as > non-inductive you would think "non-inductive" wouldn't you. I guess I'll > have to dig around in some old junk boxes or parallel several 1 watters to > get them to work. > I appreciate your information. > Ken Crazy idea but I'll throw it out here anyway. We know that carbon film resistors have some worriable inductance at 6 meters. If a guy were to take a group of say 1-watters to make up the power rating, could you count on the consistency of the outer markings to the extent that you could group them somehow in parallel/inverted so that they cancel each other's inductance in this application? -Bill Article: 93578 of rec.radio.amateur.homebrew From: dplatt@radagast.org (Dave Platt) Subject: Re: How can a wire wound reisitor be non-inductive? Date: Mon, 11 Jul 2005 04:13:30 -0000 Message-ID: <11d3sfahhkb36a9@corp.supernews.com> References: In article , KC4IH wrote: >Thanks Ralph, that is what I was thinking but when they are advertised as >non-inductive you would think "non-inductive" wouldn't you. I guess I'll >have to dig around in some old junk boxes or parallel several 1 watters to >get them to work. >I appreciate your information. Check out the Caddock and Vishay noninductive metal-foil resistors. As I understand it they use a serpentine-path foil pattern, which cancels out the inductance quite nicely. Some of them are advertised as having an inductance equivalent to an equal-length piece of wire. They're available in packages such as TO-220, and can be attached directly to a heatsink (no insulator required). -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! Article: 93579 of rec.radio.amateur.homebrew From: Paul Keinanen Subject: Re: How can a wire wound reisitor be non-inductive? Message-ID: References: Date: Mon, 11 Jul 2005 10:44:22 +0300 On Sun, 10 Jul 2005 21:21:34 -0400, "KC4IH" wrote: >I need to build a 3db pad, 50 ohm, 10 watt, to reduce the drive to my 6 >meter amp. I need 2 X 300 ohms and 1 X 18 Ohm resistors and thought it would >be an easy matter to find them with enough current rating to do the job but >can't find anything larger than 1 watt carbon (not film, which are somewhat >inductive ) resistors. I can find want is called non-inductive wire wound >resistors. I can't understand how a wire wound resistor can be >non-inductive. Could someone explain this? Look up for bifilar winding. If your exciter is reasonably clean so that you do not think about proper termination also for the harmonics, you just need an attenuator for a single frequency, which should simplify things a bit. Even if a "non-inductive" resistor has some inductance at 50 MHz, it should not be too hard to compensate for the inductance and turn the system into a very lossy series resonant circuit, in which the impedance is dominated by the resistance in the area around the resonance. An other alternative would be to put a capacitor in parallel with the resistor to form a parallel resonant circuit at 50 MHz and the actual resistance would heavily damp the resonance. If the inductance is sufficiently low, you will end up with capacitances that are practical (i.e. not affected too much by stray capacitances). This kind of approach should work at a single frequency(band), but if multiple bands are needed or if the harmonics also needs to be correctly matched, this approach does not work. Paul OH3LWR Article: 93580 of rec.radio.amateur.homebrew Date: Mon, 11 Jul 2005 04:36:23 -0400 From: -ex- Subject: Re: How can a wire wound reisitor be non-inductive? References: Message-ID: <38247$42d22f8b$4232bd49$21611@COQUI.NET> > On Sun, 10 Jul 2005 21:21:34 -0400, "KC4IH" > wrote: > > >>I need to build a 3db pad, 50 ohm, 10 watt, to reduce the drive to my 6 >>meter amp. I need 2 X 300 ohms and 1 X 18 Ohm resistors and thought it would >>be an easy matter to find them with enough current rating to do the job but >>can't find anything larger than 1 watt carbon (not film, which are somewhat >>inductive ) resistors. I can find want is called non-inductive wire wound >>resistors. I can't understand how a wire wound resistor can be >>non-inductive. Could someone explain this? I found a graph that I copied off the web sometime back showing the reactance of various R vs freq for metal film resistors. The 10-1000 ohm range of resistors show as being dead flat at 50 MHz compared to DC...and well beyond. Above and below values tend to go nuts with frequency, the high >100k values in particular. I don't remember where I found this graph but based on it I'd think you have a good chance of making those particular values work using garden variety ten-cent 1-watt resistors...thinking along the lines that manufacturing of plain old carbon film resistors would follow the same trend. I think its worth a try. -Bill Article: 93581 of rec.radio.amateur.homebrew From: straydog Subject: Re: How big has Somerset, PA hamfest been in the past? Date: Mon, 11 Jul 2005 10:07:59 +0000 Message-ID: References: On Wed, 6 Jul 2005, Bill Smith wrote: > Date: Wed, 6 Jul 2005 16:07:14 -0400 > From: Bill Smith > Newsgroups: rec.radio.swap, rec.radio.amateur.boatanchors, > rec.radio.amateur.equipment, rec.radio.amateur.homebrew > Subject: Re: How big has Somerset, PA hamfest been in the past? > > > "straydog" wrote in message > news:Pine.NEB.4.62.0506261856170.28426@sdf.lonestar.org... >> >> >> On Fri, 24 Jun 2005, Galen Watts wrote: >> >>> Date: Fri, 24 Jun 2005 08:25:27 -0400 >>> From: Galen Watts >>> To: straydog >>> Newsgroups: rec.radio.swap, rec.radio.amateur.boatanchors, >>> rec.radio.amateur.equipment, rec.radio.amateur.homebrew >>> Subject: Re: How big has Somerset, PA hamfest been in the past? >>> >>> straydog wrote: >>>> >>>> I think July 17, is the next Somerset PA hamfest and I've been thinking >>>> about going. Its a long drive from here (southern Delaware) and I was >>>> wondering how big and how good it has been in the past. Anyone got any >>>> recollections from the past? >>>> >>>> Art, w4pon >>> >>> They have pictures of last year's fest at >>> http://www.k3smt.org/hf2004/ >>> >>> -W8LNA >>> >> >> Thanks for the info... >> >> I had a look. >> >> W4PON >> >> > > Hello Art, > This is only our second annual hamfest. Last year it was held in August, a > day after the hurricane came thru. Our turnout was only about 300. Feedback > so far this year says we should have between 500-750. Good odds for winning > a door prize or the main drawing. > Worst case, we're only 6 miles from the 9/11 Flight 93 Crash Site / > Memorial. That in itself would make the trip worth it. The Somerset > Somerfest is also running from Friday thru Sunday. Food, Music, Fun... I > should work for the Chamber of Commerce...HiHi > > Hope to see you here. > Bill kb3gun > http://www.k3smt.org > > > Thanks for the further information. However, here is my problem: first, for me its a long drive one way (5-6 hours and I'd have to stay in a motel Sat night, come back home Sunday, PM). Then, I was driving around yesterday and the bigger problem: sticker shock at the gas pump (I was gazing at a sign that showed $2.30+/gal for low test regular) . I'd be spending more money on gas for the round trip than I'd expect to spend on goodies, toys, parts, etc at the fest itself. :-( Art W4PON Article: 93582 of rec.radio.amateur.homebrew From: "Dale Parfitt" References: Subject: Re: How can a wire wound reisitor be non-inductive? Message-ID: Date: Mon, 11 Jul 2005 13:01:19 GMT "KC4IH" wrote in message news:K5GdnZRYW-cFVEzfRVn-gg@adelphia.com... > I need to build a 3db pad, 50 ohm, 10 watt, to reduce the drive to my 6 > meter amp. I need 2 X 300 ohms and 1 X 18 Ohm resistors and thought it would > be an easy matter to find them with enough current rating to do the job but > can't find anything larger than 1 watt carbon (not film, which are somewhat > inductive ) resistors. I can find want is called non-inductive wire wound > resistors. I can't understand how a wire wound resistor can be > non-inductive. Could someone explain this? > > Wind up approx 40' of RG-174 into a small coil and tie wrap it. It will handle 100W + at 50 MHz and have a great return loss. Lots easier than fooling around with resistors of questionable characteristics and heating problems. Dale W4OP Article: 93583 of rec.radio.amateur.homebrew From: "JB" Subject: Re: How can a wire wound reisitor be non-inductive? Date: Mon, 11 Jul 2005 06:46:02 -0700 Message-ID: References: Use a length of lossy coax for only 3 db. A lot cheaper. None of the non-inductive wirewound or laser cut resistors will be truly non- inductive at those frequencies. Realize that the values need not be exact, because return loss will keep the SWR down. If you can't get Carbon, Use the coax. You might also want to adjust Drive or ALC in the amp. The Collins 30L-1 used to come with a length of lossy coax for this reason. ac6tk http://tekstuff.freespaces.com "KC4IH" wrote in message news:K5GdnZRYW-cFVEzfRVn-gg@adelphia.com... > I need to build a 3db pad, 50 ohm, 10 watt, to reduce the drive to my 6 > meter amp. I need 2 X 300 ohms and 1 X 18 Ohm resistors and thought it would > be an easy matter to find them with enough current rating to do the job but > can't find anything larger than 1 watt carbon (not film, which are somewhat > inductive ) resistors. I can find want is called non-inductive wire wound > resistors. I can't understand how a wire wound resistor can be > non-inductive. Could someone explain this? > > > Article: 93584 of rec.radio.amateur.homebrew From: "JB" Subject: Re: Why don't many high power RF transistor amplifiers use emitter stabilizing resistor and AC by-pass capacitors? Date: Mon, 11 Jul 2005 06:51:36 -0700 Message-ID: References: > Most RF power transistors in the 50-100 watt range already have an > internal emitter resistor. It's usually less than a tenth of an ohm, > perhaps only a few hundreths of an ohm. Its purpose is to prevent > thermal runaway and make the device more tolerant of overload due to > momentary impedance mismatches. Internal resistors have an extemely > low inductance. They are NOT wirewound. They are an integral part of > the transistor construction and material. The manufacturer may not > mention their existence in his catalogue or data book. > > RF power transistors are usually multi-emitter devices - all in > parallel. Each emitter has its own individual series resistor. > > Such low-value external resistors are not available as discrete > wire-ended circuit components. Inductance would be too high at HF and > an invitation to self oscillation. Don't attempt to use normal circuit > components in emitter leads unless a transistor manufacturer > specifically recommends them. > > HF and VHF power transistors are very fast fuses. They are worked very > close to their maximum voltage and current ratings. > ---- > Reg, G4FGQ > yup! Article: 93585 of rec.radio.amateur.homebrew From: "Bill KB3GUN" References: <42BBFBB7.20706@nrao.edu> <42cc39e2$0$52206$ec3e2dad@news.usenetmonster.com> Subject: Re: How big has Somerset, PA hamfest been in the past? Date: Mon, 11 Jul 2005 10:58:02 -0400 Message-ID: <42d288da$0$52197$ec3e2dad@news.usenetmonster.com> "straydog" wrote in message news:Pine.NEB.4.62.0507111002200.21971@mx.freeshell.org... > > > On Wed, 6 Jul 2005, Bill Smith wrote: > >> Date: Wed, 6 Jul 2005 16:07:14 -0400 >> From: Bill Smith >> Newsgroups: rec.radio.swap, rec.radio.amateur.boatanchors, >> rec.radio.amateur.equipment, rec.radio.amateur.homebrew >> Subject: Re: How big has Somerset, PA hamfest been in the past? >> >> "straydog" wrote in message >> news:Pine.NEB.4.62.0506261856170.28426@sdf.lonestar.org... >>> >>> >>> On Fri, 24 Jun 2005, Galen Watts wrote: >>> >>>> Date: Fri, 24 Jun 2005 08:25:27 -0400 >>>> From: Galen Watts >>>> To: straydog >>>> Newsgroups: rec.radio.swap, rec.radio.amateur.boatanchors, >>>> rec.radio.amateur.equipment, rec.radio.amateur.homebrew >>>> Subject: Re: How big has Somerset, PA hamfest been in the past? >>>> >>>> straydog wrote: >>>>> >>>>> I think July 17, is the next Somerset PA hamfest and I've been >>>>> thinking >>>>> about going. Its a long drive from here (southern Delaware) and I was >>>>> wondering how big and how good it has been in the past. Anyone got any >>>>> recollections from the past? >>>>> >>>>> Art, w4pon >>>> >>>> They have pictures of last year's fest at >>>> http://www.k3smt.org/hf2004/ >>>> >>>> -W8LNA >>>> >>> >>> Thanks for the info... >>> >>> I had a look. >>> >>> W4PON >>> >>> >> >> Hello Art, >> This is only our second annual hamfest. Last year it was held in August, >> a >> day after the hurricane came thru. Our turnout was only about 300. >> Feedback >> so far this year says we should have between 500-750. Good odds for >> winning >> a door prize or the main drawing. >> Worst case, we're only 6 miles from the 9/11 Flight 93 Crash Site / >> Memorial. That in itself would make the trip worth it. The Somerset >> Somerfest is also running from Friday thru Sunday. Food, Music, Fun... I >> should work for the Chamber of Commerce...HiHi >> >> Hope to see you here. >> Bill kb3gun >> http://www.k3smt.org >> >> >> > > Thanks for the further information. However, here is my problem: first, > for me its a long drive one way (5-6 hours and I'd have to stay in a > motel Sat night, come back home Sunday, PM). Then, I was driving around > yesterday and the bigger problem: sticker shock at the gas pump (I was > gazing at a sign that showed $2.30+/gal for low test regular) . I'd be > spending more money on gas for the round trip than I'd expect to spend on > goodies, toys, parts, etc at the fest itself. :-( > > > > Art > W4PON > I understand completely, Art. I'm in the same boat when it comes to distant hamfests. I have to run premium in my jeep and it's running $2.50 now. Thanks anyway for you interest. 73 Bill kb3gun Somerset PA Hamfest http://www.k3smt.org/hamfest Article: 93586 of rec.radio.amateur.homebrew From: straydog Subject: Re: How big has Somerset, PA hamfest been in the past? Date: Mon, 11 Jul 2005 22:21:48 +0000 Message-ID: References: On Mon, 11 Jul 2005, Bill KB3GUN wrote: > Date: Mon, 11 Jul 2005 10:58:02 -0400 > From: Bill KB3GUN > Reply-To: Bill KB3GUN > Newsgroups: rec.radio.swap, rec.radio.amateur.boatanchors, > rec.radio.amateur.equipment, rec.radio.amateur.homebrew > Subject: Re: How big has Somerset, PA hamfest been in the past? > > > "straydog" wrote in message > news:Pine.NEB.4.62.0507111002200.21971@mx.freeshell.org... >> >> >> On Wed, 6 Jul 2005, Bill Smith wrote: >> >>> Date: Wed, 6 Jul 2005 16:07:14 -0400 >>> From: Bill Smith >>> Newsgroups: rec.radio.swap, rec.radio.amateur.boatanchors, >>> rec.radio.amateur.equipment, rec.radio.amateur.homebrew >>> Subject: Re: How big has Somerset, PA hamfest been in the past? >>> >>> "straydog" wrote in message >>> news:Pine.NEB.4.62.0506261856170.28426@sdf.lonestar.org... >>>> >>>> >>>> On Fri, 24 Jun 2005, Galen Watts wrote: >>>> >>>>> Date: Fri, 24 Jun 2005 08:25:27 -0400 >>>>> From: Galen Watts >>>>> To: straydog >>>>> Newsgroups: rec.radio.swap, rec.radio.amateur.boatanchors, >>>>> rec.radio.amateur.equipment, rec.radio.amateur.homebrew >>>>> Subject: Re: How big has Somerset, PA hamfest been in the past? >>>>> >>>>> straydog wrote: >>>>>> >>>>>> I think July 17, is the next Somerset PA hamfest and I've been >>>>>> thinking >>>>>> about going. Its a long drive from here (southern Delaware) and I was >>>>>> wondering how big and how good it has been in the past. Anyone got any >>>>>> recollections from the past? >>>>>> >>>>>> Art, w4pon >>>>> >>>>> They have pictures of last year's fest at >>>>> http://www.k3smt.org/hf2004/ >>>>> >>>>> -W8LNA >>>>> >>>> >>>> Thanks for the info... >>>> >>>> I had a look. >>>> >>>> W4PON >>>> >>>> >>> >>> Hello Art, >>> This is only our second annual hamfest. Last year it was held in August, >>> a >>> day after the hurricane came thru. Our turnout was only about 300. >>> Feedback >>> so far this year says we should have between 500-750. Good odds for >>> winning >>> a door prize or the main drawing. >>> Worst case, we're only 6 miles from the 9/11 Flight 93 Crash Site / >>> Memorial. That in itself would make the trip worth it. The Somerset >>> Somerfest is also running from Friday thru Sunday. Food, Music, Fun... I >>> should work for the Chamber of Commerce...HiHi >>> >>> Hope to see you here. >>> Bill kb3gun >>> http://www.k3smt.org >>> >>> >>> >> >> Thanks for the further information. However, here is my problem: first, >> for me its a long drive one way (5-6 hours and I'd have to stay in a >> motel Sat night, come back home Sunday, PM). Then, I was driving around >> yesterday and the bigger problem: sticker shock at the gas pump (I was >> gazing at a sign that showed $2.30+/gal for low test regular) . I'd be >> spending more money on gas for the round trip than I'd expect to spend on >> goodies, toys, parts, etc at the fest itself. :-( >> >> >> >> Art >> W4PON >> > > I understand completely, Art. I'm in the same boat when it comes to distant > hamfests. I have to run premium in my jeep and it's running $2.50 now. > > Thanks anyway for you interest. > > 73 > Bill kb3gun > Somerset PA Hamfest > http://www.k3smt.org/hamfest Well, thanks again. FWIW, it sure would be nice if for some of these fests someone could go around, at the end, with a video camera or d-cam and take pictures (something like for that URL of the last one) of the unsold major stuff (and maybe guys selling parts?) and post these on the club website as a "possibly still available" item and an email address (or something like that). All a guy would need is: a cardstock with price and email address in felt tip pen ink, held in front of the gear. That shouldn't be too hard, or the guy selling the stuff could provide his own jpeg images on a floppy disk. I'm not particularly interested in eBay/auctionering stuff (since you have to play the escalating price game, then the shipping question, etc). But, if a guy said "Here is X, I'd like Y dollars for it, and subject to negotiations" I could get more interested in this. Art, W4PON Article: 93589 of rec.radio.amateur.homebrew From: Allodoxaphobia Subject: Re: SP-600 Transmitter project Date: 12 Jul 2005 15:19:53 GMT Message-ID: References: On Mon, 11 Jul 2005 18:06:13 -0400, GBrown wrote: > Any one have a suggestion as to a model number for this homebrew xmtr? > Something along the line that will go good with "SP-600" 006-PS ? It does sound like a fun and creative project. gl. Jonesy -- Marvin L Jones | jonz | W3DHJ | linux Pueblo, Colorado | @ | Jonesy | OS/2 __ 38.24N 104.55W | config.com | DM78rf | SK Article: 93590 of rec.radio.amateur.homebrew From: "Dave" References: Subject: Re: SP-600 Transmitter project Message-ID: <1121186639.c6617136487cc476519a22f2267db457@meganetnews2> Date: Tue, 12 Jul 2005 09:43:56 -0700 "GBrown" wrote in message news:tbudndlEEerLcE_fRVn-hw@gwi.net... >I just got done restoring an SP-600JX-1. I am now looking for an SP-600 > front panel, side supports and the two window escutcheons. The reason > being......... I am going to reverse the panel and build an AM transmitter > using the reverse panel as the front panel to the home brew transmitter. > Thinking about a single 813 with maybe some 6146's as modulator. I don't > care what the condition of the panel is. I would also like to find some > SP-600 knobs. I am going to use a VFO from a junker HT-37 and just run 75 > and 40 meter AM/CW. I think this is going to be a fun project. Any one > have > a suggestion as to a model number for this homebrew xmtr? Something along > the line that will go good with "SP-600" Neat project! Call it TX-600 or HB-600 ("Home Brew") Article: 93591 of rec.radio.amateur.homebrew From: Curious George Subject: How to build an amplifier chassis???? Date: Tue, 12 Jul 2005 12:56:09 -0400 Message-ID: I've seen several books that detail the electronic how to when it comes to building an HF RF amplifier from 100 watts to 2 KW. Great! They also show the amps sitting in these finely crafted metal cabinets. Ok well.... I don't know how to build a nice metal cabinet, and the books don't tell me. So....Now that I've decided I really want to build one of those nice home brew amps I need to know how to make the metal cabinet to put all those electronic parts in. Is there a book or web page that teaches how to build a nice metal cabinet to put those homebrew amplifiers in? Curious George Article: 93592 of rec.radio.amateur.homebrew From: "Mike Andrews" Subject: Re: How to build an amplifier chassis???? Date: Tue, 12 Jul 2005 20:19:18 +0000 (UTC) Message-ID: References: <1121188743.628871.171620@z14g2000cwz.googlegroups.com> Tim Shoppa wrote: > In the traditional world, the chassis and enclosure are related but > separate items. The common technique is: > 1. Electronics built on aluminum chassis box. Available > pre-fabricated from Hammond etc. Or make your own from sheet metal. > 2. Front panel bolted to the chassis box. Knobs and switches and > meters go on the front panel. And are either wired to the stuff inside > the chassis or control variable caps etc. on the chassis via long > shafts. Front panel for a big project is often 19" wide rack-mount > panel (again a standard size available from Hammond et al.) > 3. Enclosure is a sheet metal box that slides on from behind. Made > using sheet metal tools. > At the high end, "sheet metal tools" are a big shear for cutting and a > brake for bending. At the low end you make you own brake out of 2x4's > and hinges, and cut with hacksaw/table saw/aircraft snips (depending on > type of cut, thickness, and material.) > For the really classy look all the holes you need can be cut with > punches. More likely for a hobbyist is drills and hacksaws and files > and the most valuable tool of all: the nibbler. And if there's a good sheet metal shop in your area (there is in mine), you may be able to get the owner to custom-make stuff for you for prices that merely make you want to scream. But that way you'll get what you want, or at least what you told the owner you wanted. My preference, when I get to indulge it, is for rackmount panels with one or more chassis boxes bolted to it, and subchassis inside those as seems appropriate. -- Mike Andrews W5EGO 5WPM mikea@mikea.ath.cx Extra Tired old sysadmin working on his code speed Article: 93593 of rec.radio.amateur.homebrew From: "Joel Kolstad" Subject: Re: Simple questions on receivers Date: Tue, 12 Jul 2005 14:01:00 -0700 Message-ID: <11d8bpfoa35o6c3@corp.supernews.com> References: <1121199166.494373.59190@g49g2000cwa.googlegroups.com> "dave.harper" wrote in message news:1121199166.494373.59190@g49g2000cwa.googlegroups.com... > How well-defined is the gain for a cap-coil loop, like in an AM radio? > (i.e., how fast does the gain droppoff as you move up or down from the > 'tuned' frequency?) Is it a function of L and C? Or just frequency? For the L-C resonator itself, the falloff will be 6dB per octave (doubling of frequency) once you're well outside of the center (tuned) frequency. The 3dB bandwidth will be determined by the Q of the circuit, and this is often not particularly well defined during the design stage -- often a well-defined bandpass filter somewhere "down the line" (e.g., at an IF stage) will ultimately define what the radio receives. The 6dB/octave drop comes from just looking at the impedance or transfer function of an LC(R) resonator -- you'll end up with an s^2 (frequency squared) term in the denominator of the equation. > (different combinations of L and C will tune to the same frequency, but > is the gain the same?) No, although for low Q resonators, it's often pretty close. > How come the coils on many of the CR schematics I've seen have multiple > tap locations? It seems that with a variable cap, you should be able > to tune to whatever frequency that's in your range. Is it to increase > the range of your radio's coverage? Or because the gain at certain > frequencies is better with different C/L combinations? They're usually trying to match the impedance of the LC circuit to the input impedance of "the next stage" (i.e., a transistor amplifier) to maximize power transfer. So, while it's not really "gain" (we haven't amplified anything yet -- this is more like a resistive divider), the output will be higher with different C/L combinations. Generally speaking, most relatively simple AM receivers are really only intended to pick up relatively strong, nearby transmitters. As such, you can get away with an awful lot of "cut and try" when it comes to designing the circuit (largely ignore matching impedances, Q's, etc.) and still obtain acceptable results. ---Joel Article: 93594 of rec.radio.amateur.homebrew From: "Jeff James" Subject: Buy and Sell your Tube Gear! Message-ID: Date: Tue, 12 Jul 2005 21:22:54 -0400 You never know what you'll find.. http://www.dealamerica.com/deal/cgi-bin/ads/bcads.cgi FREE ads Dedicated to Vintage Amateur Radio... Article: 93595 of rec.radio.amateur.homebrew From: Jim Subject: Why does a change in jumper length change amplifer outout? Message-ID: <8cv8d11adq3khsi653abthf78u126399ta@4ax.com> Date: Wed, 13 Jul 2005 02:42:56 GMT I have an external RF transistor amplifier (AB1) using 2 MRF455 transistors in common emitter mode. I have a resistive T pad with an approximate impedance of 50 ohms on the input side of the transistors. The SWR on the input of the amp shows 1.3:1. When I use a 2 foot jumper between the radio and the amp the amp puts out about 100 watts max, but when I switch to a 9 foot jumper the amp puts out about 40 watts max. The receive stays the same no matter which jumper is used. Why does changing the length of the jumper between the radio and the amp make such a drastic change in how much the amp puts out? Article: 93596 of rec.radio.amateur.homebrew From: Bob Liesenfeld Subject: Re: Why does a change in jumper length change amplifer outout? Date: Tue, 12 Jul 2005 21:56:22 -0500 Message-ID: <42D482D6.CC5E4879@visi.com> References: <8cv8d11adq3khsi653abthf78u126399ta@4ax.com> Jim wrote: > > I have an external RF transistor amplifier (AB1) using 2 MRF455 > transistors in common emitter mode. What type of cable and connectors are the two jumpers? Article: 93597 of rec.radio.amateur.homebrew From: Jim Subject: Re: Why does a change in jumper length change amplifer outout? Message-ID: References: <8cv8d11adq3khsi653abthf78u126399ta@4ax.com> <42D482D6.CC5E4879@visi.com> Date: Wed, 13 Jul 2005 03:10:41 GMT On Tue, 12 Jul 2005 21:56:22 -0500, Bob Liesenfeld wrote: > > >Jim wrote: > >> >> I have an external RF transistor amplifier (AB1) using 2 MRF455 >> transistors in common emitter mode. > > What type of cable and connectors are the two jumpers? RG-58 cable with PL-259 connectors. Article: 93598 of rec.radio.amateur.homebrew From: tim gorman Subject: Re: Why does a change in jumper length change amplifer outout? References: <8cv8d11adq3khsi653abthf78u126399ta@4ax.com> Message-ID: <3b12bd.52j.ln@tg6124.ab0wr.net> Date: Tue, 12 Jul 2005 22:21:07 -0500 Jim wrote: > > > > I have an external RF transistor amplifier (AB1) using 2 MRF455 > transistors in common emitter mode. I have a resistive T pad with an > approximate impedance of 50 ohms on the input side of the transistors. > The SWR on the input of the amp shows 1.3:1. When I use a 2 foot > jumper between the radio and the amp the amp puts out about 100 watts > max, but when I switch to a 9 foot jumper the amp puts out about 40 > watts max. The receive stays the same no matter which jumper is used. > Why does changing the length of the jumper between the radio and the > amp make such a drastic change in how much the amp puts out? Are you sure the 9 foot jumper is good? What frequency is this occurring at? Is the SWR 1.3:1 for both jumpers? Measure the SWR, forward power, and reflected power levels at the transmitter end for both jumpers and then measure it at the amplifier end for both jumpers. See if everything stays the same for both jumpers. Do you have an RF probe you can use to measure the voltages at each end of the link? Unless you are using rg174 the 7 foot of extra cable should not make this much difference unless the input impedance of the amplifer is not 50ohm resistive. If it is not purely resistive then changing the cable length can impact the SWR seen at the transmitter end significantly. This could cause foldback in the RF amplifier in the transmitter thus affecting the output of the amplifier. This would all be seen in the measurements of SWR, forward power, and reflected power levels in the measurements above. Let us know what you find. tim ab0wr Article: 93599 of rec.radio.amateur.homebrew From: Roy Lewallen Subject: Re: Why does a change in jumper length change amplifer outout? Date: Tue, 12 Jul 2005 21:39:44 -0700 Message-ID: <11d96oksfgpfa03@corp.supernews.com> References: <8cv8d11adq3khsi653abthf78u126399ta@4ax.com> <3b12bd.52j.ln@tg6124.ab0wr.net> tim gorman wrote: > . . . > Unless you are using rg174 the 7 foot of extra cable should not make this > much difference unless the input impedance of the amplifer is not 50ohm > resistive. If it is not purely resistive then changing the cable length can > impact the SWR seen at the transmitter end significantly. . . Changing the cable length won't change the SWR on the cable regardless of the kind of load impedance and, if the SWR meter is designed for the cable's Z0, it won't change the SWR meter reading, either. Except, of course, that cable loss will always lower the SWR -- but that shouldn't be a significant factor with such short cables. Changing the cable length *will* change the impedance looking into the cable, whether or not the load is purely resistive. The only exception to this is if the load is resistive *and equal to the line's characteristic impedance* in which case the impedance looking in will be Z0 for any length cable. Transmitters will often put up with some mismatched impedances better than others, even if the SWR is the same, and sometimes changing the cable length between it and a mismatched load will cause it to see a more or less favorable impedance. But if the SWR really is 1.3:1, I doubt that's the cause of this problem. I agree with the suggestion that the OP measure the SWR and if possible the power at both ends with both cables. Something else is going on, like maybe a bad cable or connector. I don't think the OP said what frequency this is happening at. That might give some additional clues. Roy Lewallen, W7EL Article: 93600 of rec.radio.amateur.homebrew From: "sean" References: <2d5631c0.0506082158.39fb1c20@posting.google.com> <42d09367_1@newspeer2.tds.net> <42d0ea2e_1@x-privat.org> Subject: Re: How to turn a radio into a time-bomb??? Date: Wed, 13 Jul 2005 04:29:25 -0400 Message-ID: <42d4d0c7$1_1@newspeer2.tds.net> I'm not talking to them. I'm talking to the one who posted this topic. Now, You can tell those whatever forces if you'd like. Why do you want someone to do what you should do yourself? "Polymath" wrote in message news:42d0ea2e_1@x-privat.org... > Tell that to the cowardly murdering bastards who make up the > unlawful invading forces in Afghanistan and in Iraq. > > "sean" wrote in message > news:42d09367_1@newspeer2.tds.net... > > Only You can choose to not HAVE to kill. > > You only choose to think to kill. > > No one else chooses for you. > > You have a choice. > > Article: 93601 of rec.radio.amateur.homebrew From: "Mike Willis" Subject: Re: Why does a change in jumper length change amplifer outout? Date: Wed, 13 Jul 2005 11:46:13 +0100 Message-ID: References: <8cv8d11adq3khsi653abthf78u126399ta@4ax.com> <3b12bd.52j.ln@tg6124.ab0wr.net> <11d96oksfgpfa03@corp.supernews.com> "Roy Lewallen" wrote in message news:11d96oksfgpfa03@corp.supernews.com... > tim gorman wrote: > > I agree with the suggestion that the OP measure the SWR and if possible > the power at both ends with both cables. Something else is going on, > like maybe a bad cable or connector. I am assuming this is VHF and if so I would say that there is a bad connector at both ends - PL259s. These are not good enough connenctors for use anywhere above HF, the are simply screened banana plugs. If this is a ready made jumper for the CB market, the cable might not be anything like 50 ohms. Mike Article: 93602 of rec.radio.amateur.homebrew From: "Joel Kolstad" Subject: Frequency multipliers: Usable modulation formats? Date: Wed, 13 Jul 2005 08:13:06 -0700 Message-ID: <11dabp5hfvvv25@corp.supernews.com> I was over on comp.dsp exposing my ignorance the other day when it eventually dawned on me that a frequency multiplier will, in the frequency domain, just convolve whatever the input signal is with itself. This got me to thinking... why is it that frequency multipliers work as well as they do for something like FM? Assuming a sine wave modulating signal, the FM spectra is a sum harmonics with amplitudes dictated by a Bessel function; frequency multiplying this would seem to add new harmonic content to the mix besides just doubling the frequency of what's already present. So... does it turn out, mathematically, that frequency multiplying an FM signal just so happens to end up what nothing more than a "frequency scaled" spectra of what was originally present? Or is some amount of distortion added in the process (assuming perfect mixers used as the frequency multipliers and the DC component of the mixers' outputs removed). I've been told that, in general, frequency multiplier can be effectively applied to most any modulation scheme that has a reasonably constant envelope, e.g., FM, PM, FSK, even QPSK. Is this generally accepted knowledge? Thanks, ---Joel Kolstad Article: 93603 of rec.radio.amateur.homebrew From: "William E. Sabin" References: <11dabp5hfvvv25@corp.supernews.com> Subject: Re: Frequency multipliers: Usable modulation formats? Message-ID: Date: Wed, 13 Jul 2005 17:10:45 GMT Suppose a 1 MHz signal is frequency modulated by a 1 kHz sine wave. The frequency deviates over some frequency range, for example +/- 5 kHz. If we put that signal into a times-ten multiplier the FM signal is at 10 MHz and the frequency deviatioon is ten times greater (+/- 50 kHz). However, the *rate* at which the 10 MHz signal traverses the greater frequency deviation is still 1 kHz. That does not change and that is what the FM detector output delivers. Bill W0IYH "Joel Kolstad" wrote in message news:11dabp5hfvvv25@corp.supernews.com... >I was over on comp.dsp exposing my ignorance the other day when it >eventually > dawned on me that a frequency multiplier will, in the frequency domain, > just > convolve whatever the input signal is with itself. This got me to > thinking... > why is it that frequency multipliers work as well as they do for something > like FM? Assuming a sine wave modulating signal, the FM spectra is a sum > harmonics with amplitudes dictated by a Bessel function; frequency > multiplying > this would seem to add new harmonic content to the mix besides just > doubling > the frequency of what's already present. So... does it turn out, > mathematically, that frequency multiplying an FM signal just so happens to > end > up what nothing more than a "frequency scaled" spectra of what was > originally > present? Or is some amount of distortion added in the process (assuming > perfect mixers used as the frequency multipliers and the DC component of > the > mixers' outputs removed). > > I've been told that, in general, frequency multiplier can be effectively > applied to most any modulation scheme that has a reasonably constant > envelope, > e.g., FM, PM, FSK, even QPSK. Is this generally accepted knowledge? > > Thanks, > ---Joel Kolstad > > Article: 93604 of rec.radio.amateur.homebrew From: LenAnderson@ieee.org Subject: Re: High Voltage Techniques Date: 13 Jul 2005 10:34:18 -0700 Message-ID: <1121276058.511776.33610@g44g2000cwa.googlegroups.com> References: <5fOdnQ8Hy6LPB0nfRVn-qw@giganews.com> From: "Bob" on Tues 12 Jul 2005 23:36 >Since Curious George asked a basic question, I will ask one also. For those >of us that are used to working with low voltage equipment, what is a good >book for learning to work with the high voltages of tubes? The "best book" is simply COMMON SENSE. Use your eyes and brain. If the voltage and current through your body in the path of the heart is above 30 Volts and greater than 30 mA, you have the approximate threashold of cardiac fibrillation...where the heart loses its normal oscillation and begins to "flutter" and not pump blood. Potentially fatal if this "30-30" rule is exceeded. DON'T GRAB LIVE HIGH VOLTAGES WITH BOTH HANDS. [guess where the heart is located in this body "circuit"?] A common mistake of the above is leaning on a conductive surface touching it somehow when probing with the other hand...the "circuit" has been completed even though it may not enter awareness. Be AWARE of the maximum voltage limitations on all your measuring equipment. If a manufacturer says "input voltage 500 V max" that IS what they mean...there's a "fudge factor" in that rating but try NOT to use it. Do not destruct expensive test machines or the circuit you're testing. THINK about what you are doing around high voltage. Thinking will enable you to continue living to think some more about other things. RESPECT high voltage. It ain't no kiddie toy to fool with. LenAnderson@ieee.org [a high voltage survivor in the biz since 1948] Article: 93605 of rec.radio.amateur.homebrew From: Roy Lewallen Subject: Re: Why does a change in jumper length change amplifer outout? Date: Wed, 13 Jul 2005 11:30:56 -0700 Message-ID: <11danf69ajpf5f1@corp.supernews.com> References: <8cv8d11adq3khsi653abthf78u126399ta@4ax.com> <3b12bd.52j.ln@tg6124.ab0wr.net> <11d96oksfgpfa03@corp.supernews.com> <1121278260.793227.217240@o13g2000cwo.googlegroups.com> LenAnderson@ieee.org wrote: > . . . > "Doubler plates" are often used in retro-fitting antennas and > other things on aircraft, just a sheet of metal to re-enforce > strength of the metal skin. The doubler plate drawings had > clearance holes just too close to type N connector sleeve > outer diameter. Connectors mated, but NOT fully. As altitude > increases, temperature drops. The not-fully mated center > conductor pin just contracted until it lost contact at cold > temps. Enlarging the doubler plate clearance hole allowed > full mating, no shrinkage of contacts. Unlikely problem > solved at about quarter to 8 PM in a cold hangar. :-( > > Sometimes the "unlikely" not-described-in-text things are to > blame. I was in Anchorage when color TV was first being broadcast there (mid-'60s) and people were using outside antennas with coax feed for the first time. The center pin of a male type F connector is just the center conductor of the RG-59 cable, and on a cold day the center conductor would shrink enough on a long cable run to pull the pin out of the female connector. Anybody who has spent some time as a technician (as I did) has a long list of tales to tell about strange problems. Among my favorites are a car with the battery installed backward (a Corvair -- car started and ran, but gauges were funky and the radio blew), and a piece of copper pipe with 300 ohms DC resistance. But those are just a couple. . . Roy Lewallen, W7EL Article: 93606 of rec.radio.amateur.homebrew From: "Jim Barnard" Subject: Murata Ceramic Filters Date: Wed, 13 Jul 2005 17:26:19 -0400 Message-ID: Does anyone know of a retail vendor that would sell the Murata ceramic filter CFJ455K5 without a $25-$5000 minimum order? I just need one piece for a Ten-tec radio. Thanks Jim Article: 93607 of rec.radio.amateur.homebrew From: dplatt@radagast.org (Dave Platt) Subject: Re: QUESTION: Cheap Accurate Shaft Position Encoder Date: Wed, 13 Jul 2005 21:47:54 -0000 Message-ID: <11db30a5vibm695@corp.supernews.com> References: <1121290111.687842.193790@g49g2000cwa.googlegroups.com> In article <1121290111.687842.193790@g49g2000cwa.googlegroups.com>, wrote: >Does anyone know of a cheap and accurate shaft encoder assembly, >suitable for that "professional rig feel" for spindle position to >frequency encoding. I'm thinking about some sort of integrated unit >that contains the encoder, code wheel, assembly, bearings etc. HP used to make very nice optical rotary encoders - e.g. the HEDS-7500 "digital potentiometer" (which has its own shaft and mounting), and the HEDS-5000 series optical encoders (which mount on an existing shaft). These are from a 1989 catalog, and the current versions or equivalents are no doubt different. www.newark.com lists a bunch of them. I would not call them "cheap". According to Digikey's catalog, Grayhill and Clarostat and Iwatsu and Bourns all make similar rotary optical encoders with reasonably high pulse-per-revolution counts (128 or 256). It looks to me as if you're probably facing a price of $40 - $60 per piece, in single quantities, for any commercially-made rotary encoder of this caliber. For anything very much less expensive, you'll probably have to homebrew something (e.g. a couple of simple interruption-type photosensors, and a code wheel laserprinted on a piece of plastic) and mount it on an existing spindle/shaft. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! Article: 93608 of rec.radio.amateur.homebrew From: Bill Janssen Subject: Re: High Voltage Techniques References: <5fOdnQ8Hy6LPB0nfRVn-qw@giganews.com> <1121276058.511776.33610@g44g2000cwa.googlegroups.com> Message-ID: Date: Thu, 14 Jul 2005 00:07:02 GMT LenAnderson@ieee.org wrote: >From: "Bob" on Tues 12 Jul 2005 23:36 > > > >>Since Curious George asked a basic question, I will ask one also. For those >>of us that are used to working with low voltage equipment, what is a good >>book for learning to work with the high voltages of tubes? >> >> > > > An RCA tube manual and the warnings as stated below. Bill K7NOM > The "best book" is simply COMMON SENSE. Use your eyes and brain. > > If the voltage and current through your body in the path of the > heart is above 30 Volts and greater than 30 mA, you have the > approximate threashold of cardiac fibrillation...where the > heart loses its normal oscillation and begins to "flutter" > and not pump blood. Potentially fatal if this "30-30" rule > is exceeded. > > DON'T GRAB LIVE HIGH VOLTAGES WITH BOTH HANDS. [guess where > the heart is located in this body "circuit"?] > > A common mistake of the above is leaning on a conductive surface > touching it somehow when probing with the other hand...the > "circuit" has been completed even though it may not enter > awareness. > > Be AWARE of the maximum voltage limitations on all your measuring > equipment. If a manufacturer says "input voltage 500 V max" > that IS what they mean...there's a "fudge factor" in that rating > but try NOT to use it. Do not destruct expensive test machines > or the circuit you're testing. > > THINK about what you are doing around high voltage. Thinking > will enable you to continue living to think some more about > other things. > > RESPECT high voltage. It ain't no kiddie toy to fool with. > > LenAnderson@ieee.org > > [a high voltage survivor in the biz since 1948] > > > Article: 93609 of rec.radio.amateur.homebrew From: Bill Janssen Subject: Re: QUESTION: Cheap Accurate Shaft Position Encoder References: <1121290111.687842.193790@g49g2000cwa.googlegroups.com> <11db30a5vibm695@corp.supernews.com> Message-ID: Date: Thu, 14 Jul 2005 00:09:24 GMT Dave Platt wrote: >In article <1121290111.687842.193790@g49g2000cwa.googlegroups.com>, > wrote: > > > >>Does anyone know of a cheap and accurate shaft encoder assembly, >>suitable for that "professional rig feel" for spindle position to >>frequency encoding. I'm thinking about some sort of integrated unit >>that contains the encoder, code wheel, assembly, bearings etc. >> >> > >HP used to make very nice optical rotary encoders - e.g. the HEDS-7500 >"digital potentiometer" (which has its own shaft and mounting), and >the HEDS-5000 series optical encoders (which mount on an existing >shaft). These are from a 1989 catalog, and the current versions or >equivalents are no doubt different. www.newark.com lists a bunch of >them. > >I would not call them "cheap". > >According to Digikey's catalog, Grayhill and Clarostat and Iwatsu and >Bourns all make similar rotary optical encoders with reasonably high >pulse-per-revolution counts (128 or 256). > >It looks to me as if you're probably facing a price of $40 - $60 per >piece, in single quantities, for any commercially-made rotary encoder >of this caliber. > >For anything very much less expensive, you'll probably have to >homebrew something (e.g. a couple of simple interruption-type >photosensors, and a code wheel laserprinted on a piece of plastic) and >mount it on an existing spindle/shaft. > > > Or take apart a computer mouse as they each have two. Bill K7NOM Article: 93610 of rec.radio.amateur.homebrew From: "Roger Leone" References: <1121290111.687842.193790@g49g2000cwa.googlegroups.com> Subject: Re: QUESTION: Cheap Accurate Shaft Position Encoder Message-ID: <1PiBe.2051$_%4.856@newssvr14.news.prodigy.com> Date: Thu, 14 Jul 2005 01:00:45 GMT Tim: There used to be a website with info on using surplus stepper motors as precision shaft encoders. I have been doing Google searches without success. Perhaps someone else will be able to provide a URL. It was Australian, I believe. Good luck. Roger K6XQ Article: 93611 of rec.radio.amateur.homebrew From: straydog Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power Date: Thu, 14 Jul 2005 01:29:21 +0000 Message-ID: References: <1121288717.540109.24910@g14g2000cwa.googlegroups.com> On Wed, 13 Jul 2005 Timothy@tholtom.freeserve.co.uk wrote: > Date: 13 Jul 2005 14:05:17 -0700 > From: Timothy@tholtom.freeserve.co.uk > Newsgroups: rec.radio.amateur.homebrew > Subject: QUESTION: Fun with Svetlanas or Staying alive with kV power supplies > > My knowledge of vacuum tubes and kV power supplies is limited. I have > been reading an article in the ARRL Handbook detailing the construction > of a 1kW HF Linear. I'd like to try my hand at building something like > this. I found the article a little intimidating: Ceramic insulators, > parasitic suppressors, thermal and mechanical engineering etc. Is > there some book that details this type of thing with an explanation of > the whys as well as the whats and hows. My priorities are: > > 1) Safety. I'd like to be alive to make my first 1kW QSO > 2) Avoiding equipment destruction, arc overs, black smoke, explosions > etc > 3) Safetly troubleshooting this kind of equipment, loading testing > etc. > 4) How to deal with tubes: warm up, care, etc... > 5) Avoiding TVI (ITV), parasitic oscillations etc. > 6) Longevity and Duty Cycle issues etc. > 7) Costs and sources. > > Hope someone can help. > > Thanks, > > Tim When I was a kid, I was building 10kV HV transformers, 100kV Tesla coils, spark coils, discharging HV capacitors that make "bangs" about as loud as medium sized firecrackers, smoked resistors, shorting outputs on 100 amp transformers just to see the sparks fly, etc., and so I have an intuitive feeling for various stuff. I've gotten shocks maybe a dozen or two times in my life. Nasty. Most of the time these were from a finger to thumb and not through my heart. When current was involved, I'd get a button of burned flesh on my skin and that really hurts plus burnt flesh really stinks like almost nothing else except dead flesh that has been dead long enough at room temperatures to really stink. RF burns...you don't feel the pain (which also really hurts) until after the burn and you get that burnt flesh stink, too. Even from 50 watt rigs they can be bad. My experience includes mechanical devices, electric drills, bolts and nuts, threaders, chassis punches, electric drills, band saws for cutting metal sheets, etc. If you have never done anything "hands on" in your life, then your grand plan dream may be an undertaking that you would be wise to avoid. On the other hand, if you are mechanically inclined and practical and NOT a klutz (definitely not a klutz), then I'd suggest starting with a smaller and easier project and then move up. At points where you start working with lethal voltages and currents, you do need to be careful. Very very careful. They say when the power is on and the cabinet is open, you need to keep one hand in one of your pockets. Stand on a piece of dry wood at least 1/2" thick, etc. Yes, arcs and smoke can be intimidating. Just the surprise from an arc can make you jump in an unpredictable way and if not hurt yourself from the electrical shock, then you'll bang your head or something else. Parasitic oscillations and TVI: At least start with a KW level dummy load and know what the book says about neutralization and how to test for it and adjust it. Also, you cannot have enough meters to measure everything. Even filament voltage and current. I'd have a meter for every circuit: plate, screen grid, control grid, cathode current, and voltages on all of them. Weirdest discoveries: serious RF noise from solid-state diodes. Also, serious RF noise from HV transformers (output connected to absolutely nothing, but AC on primary and can hear the noise across the SW band). Weirdest lightning effect: blew out a very big (1 kW) plate transformer (2200-0-2200 v) and bypass capacitors to ground and nothing else in the hamshack was affected (collins S line, Drake twins, ten tec rig, etc.). Key warning: know what you can and can't get away with using HV silicon diodes. Building your own gear: I have had no sense of pride, accomplishment, and usefulness like building my own. Especially from junk in the junk box. My biggest rigs were 500 watt linears using 4-400As, and a few others. Built kits (Knight, Heath [too bad they are not around any more]), too. W4PON Article: 93612 of rec.radio.amateur.homebrew From: et472@FreeNet.Carleton.CA (Michael Black) Subject: Re: QUESTION: Cheap Accurate Shaft Position Encoder Date: 14 Jul 2005 02:03:58 GMT Message-ID: References: <1121290111.687842.193790@g49g2000cwa.googlegroups.com> <1PiBe.2051$_%4.856@newssvr14.news.prodigy.com> "Roger Leone" (raleoneTAKEOUT@sbcglobal.net) writes: > Tim: > > There used to be a website with info on using surplus stepper motors as > precision shaft encoders. I have been doing Google searches without > success. Perhaps someone else will be able to provide a URL. It was > Australian, I believe. > > Good luck. > > Roger K6XQ > > There was an article in "Radio Electronics" (or maybe it had morphed into "Electronics Now" by that point), I'd say around 1994 or so. The concept isn't much more than taking the outputs of the stepper and putting them through comparators to get a binary waveform. But of course, picking the right stepper is important since you need the fine steps, and I know when I brought this up before, someone had something to say against the concept, though I sure can't remember what they felt was wrong with the concept. Michael VE2BVW Article: 93613 of rec.radio.amateur.homebrew From: Ken Scharf Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power References: <1121288717.540109.24910@g14g2000cwa.googlegroups.com> Message-ID: Date: Wed, 13 Jul 2005 22:34:03 -0400 Timothy@tholtom.freeserve.co.uk wrote: > My knowledge of vacuum tubes and kV power supplies is limited. I have > been reading an article in the ARRL Handbook detailing the construction > of a 1kW HF Linear. I'd like to try my hand at building something like > this. I found the article a little intimidating: Ceramic insulators, > parasitic suppressors, thermal and mechanical engineering etc. Is > there some book that details this type of thing with an explanation of > the whys as well as the whats and hows. My priorities are: > > 1) Safety. I'd like to be alive to make my first 1kW QSO > 2) Avoiding equipment destruction, arc overs, black smoke, explosions > etc > 3) Safetly troubleshooting this kind of equipment, loading testing > etc. > 4) How to deal with tubes: warm up, care, etc... > 5) Avoiding TVI (ITV), parasitic oscillations etc. > 6) Longevity and Duty Cycle issues etc. > 7) Costs and sources. > > Hope someone can help. > > Thanks, > > Tim > I built a homebrew KW about 15 years ago using a pair of 4-400 in grounded grid. It worked fine on 80-20 but I never did get the tank Q adjusted well enough for good output above that. Not that it couldn't have been done with a bit more tinkering. The power supply put out about 4000 volts no load. I used a time delay circuit with a relay and a power resistor to limit the in-rush current while the capacitor filter bank charged. It had a relay whose ac coil was across the primary of the plate transformer that shorted out a power resistor in series with the primary. As the caps charged and the input current fell so did the voltage drop across the power resistor until the primary voltage rose to the relay's pull in voltage shorting out the resistor. (Idea from ARRL HB). A second time delay circuit did the same thing for the filaments of the 4-400's. This relay also locked out a second relay that applied power to the plate transformer. Result, the plate supply couldn't be turned on until the 4-400 filaments were warm, that delay was about 1-2 seconds during which a power resistor in the filament transformer primary limited the 4-400 filaments to half voltage. The filter caps were 10 330uf 450v computer grade units in series, each cap bridged by a 50k 25W power resistor to even the voltage across the caps and act as a bleeder resistor. A 1ma meter with a suitable multiplier resistor in series served as a voltmeter across the capacitors (I forget how many meg ohm it was). The meter case was thick enough plastic to be insulated enough from the chassis (and and besides the main plumbing was behind several meg ohms). The meter read 5000v full scale. I always assumed there was voltage across the caps when I worked on the rig. First pull the plug(s). Wait till the voltmeter drops to zero. THEN put a heavy screwdriver with a well insulated handle from ground to the HV terminal to be sure! (I used to do that to picture tubes when working on tv sets). Keep on hand in the pocket if you need to adjust anything when it's hot. BTW an RF burn can be more deadly than a DC jolt. (Think microwave oven). HV isn't the only thing that can get you. High current can give you a nasty surprise. Like the guy replacing some batteries on a golf cart. He was using a ratchet wrench to tighten the battery clamps and he ended on the most positive battery terminal. The handle of the wrench hit the chassis of the golf cart putting it between 36 volts and ground of some VERY HEAVY DUTY batteries. Ever see a Sears ratchet wrench glow WHITE HOT? (and melt?) Article: 93614 of rec.radio.amateur.homebrew From: "AAA RF Products" Subject: Coax Cable, Connector & Adapter Catalog Message-ID: Date: Wed, 13 Jul 2005 20:14:47 -0700 Please email or call for your free copy of our latest coax connector, adapter, cable assembly & bulk coaxial cable catalog. No minimum order No handling fees. email: sales@aaarfproducts.com call: 949 481 3154 fax: 949 388 5448 mail: AAA RF Products, 949 Calle Amanecer, San Clemente, CA 92673 USA Article: 93615 of rec.radio.amateur.homebrew From: Roy Lewallen Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power Date: Thu, 14 Jul 2005 00:48:01 -0700 Message-ID: <11dc65rbamb6qf2@corp.supernews.com> References: <1121288717.540109.24910@g14g2000cwa.googlegroups.com> straydog wrote: > . . . > arcs and smoke can be intimidating. Just the surprise from an arc can > make you jump in an unpredictable way and if not hurt yourself from the > electrical shock, then you'll bang your head or something else. . . In a previous life, I was reaching way to the back of a cabinet of radar equipment for some reason. I was lying on my stomach, my arm was extended all the way, and my head was into the cabinet doorway about at the forehead level, with a couple of inches clearance above and below. Of course all the safety precautions were followed -- some of the heavy ground radar stuff I worked on was easily lethal. But there was some charged capacitor, something hot from another cabinet of gear, I don't recall, and I got a minor shock. My instinctive reaction was to jerk my head up, and it hit the top of the doorway. That hurt and made me reflexively jerk my head downward, hitting the bottom of the doorway with my forehead. That caused a jerk back upward, hitting the top again, and so forth. There I was, oscillating up and down, beating my head to a pulp, knowing exactly what was happening but helpless to do anything about it. It continued for what seemed like a long time, until I was sore enough that I couldn't feel one more whack, when I was finally able to stop and extract my head and arm. I guess I've felt as stupid a few times since, but only a few times. And when you bend your arm every which way in order to get at something, it might go in all twisted contorted, but it comes out fast and straight when you get bit. I've lost a bit of skin that way, too. Roy Lewallen, W7EL Article: 93616 of rec.radio.amateur.homebrew From: Roy Lewallen Subject: Re: Class C amplifier Date: Thu, 14 Jul 2005 01:02:12 -0700 Message-ID: <11dc709s7hv8273@corp.supernews.com> References: <1121320385.670687.309640@g44g2000cwa.googlegroups.com> rkrishnan wrote: > I am reading through the excellent book "Solid State Design" by Wes > Hayward et al. I have a specific question on Class C amplifier. On > chapter 2 Fig 15, a Clas C amplifier is shown with a buffer amplifier > link coupled in front. > > Why is link coupling needed here, can't the collector be directly > connected to the base? It is for impedance matching or is there any > other motives behind this structure? It's for impedance matching. As usual, there are several ways it can be done, each with its own advantages and disadvantages. That method is probably the simplest for the particular application, but you have to watch the flux density in the transformer primary if it's wound on a ferrite core with no air gap (such as a toroid core) and make sure the D.C. current won't cause core saturation. Other methods allow you to separate the RF choke from the transformer, like in Fig. 16, so you can optimize the RF choke for its job and the transformer for its job. Or you can use several types of LC network to do the job. Roy Lewallen, W7EL Article: 93617 of rec.radio.amateur.homebrew Message-ID: <42D64EAD.9090207@invalid.invalid> From: Doug Smith W9WI Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power References: <1121288717.540109.24910@g14g2000cwa.googlegroups.com> Date: Thu, 14 Jul 2005 11:38:29 GMT Ken Scharf wrote: > The filter caps were 10 330uf 450v computer grade units in series, each Probably dumb (and WAY off topic) question: What's the *intended* purpose of a 450v "computer grade" capacitor? -- Doug Smith W9WI Pleasant View (Nashville), TN EM66 http://www.w9wi.com Article: 93618 of rec.radio.amateur.homebrew From: straydog Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power Date: Thu, 14 Jul 2005 11:45:41 +0000 Message-ID: References: <1121288717.540109.24910@g14g2000cwa.googlegroups.com> On Thu, 14 Jul 2005, Roy Lewallen wrote: > Date: Thu, 14 Jul 2005 00:48:01 -0700 > From: Roy Lewallen > Newsgroups: rec.radio.amateur.homebrew > Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power > supplies > > straydog wrote: >> . . . >> arcs and smoke can be intimidating. Just the surprise from an arc can make >> you jump in an unpredictable way and if not hurt yourself from the >> electrical shock, then you'll bang your head or something else. . . > > In a previous life, I was reaching way to the back of a cabinet of radar > equipment for some reason. I was lying on my stomach, my arm was extended all > the way, and my head was into the cabinet doorway about at the forehead > level, with a couple of inches clearance above and below. Of course all the > safety precautions were followed -- some of the heavy ground radar stuff I > worked on was easily lethal. But there was some charged capacitor, something > hot from another cabinet of gear, I don't recall, and I got a minor shock. My > instinctive reaction was to jerk my head up, and it hit the top of the > doorway. That hurt and made me reflexively jerk my head downward, hitting the > bottom of the doorway with my forehead. That caused a jerk back upward, > hitting the top again, and so forth. There I was, oscillating up and down, > beating my head to a pulp, knowing exactly what was happening but helpless to > do anything about it. It continued for what seemed like a long time, until I > was sore enough that I couldn't feel one more whack, when I was finally able > to stop and extract my head and arm. I guess I've felt as stupid a few times > since, but only a few times. > > And when you bend your arm every which way in order to get at something, it > might go in all twisted contorted, but it comes out fast and straight when > you get bit. I've lost a bit of skin that way, too. > > Roy Lewallen, W7EL > Yep. Great story. Reminds me about that sad/funny joke about the guy, his tower, bucket of tools in a wooden barrel, ropes, pully, and somehow he goes up and down the tower, wooden barrel breaks so the counterweight disappears and he goes down again....broken bones, cracked skull, all kinds of hospital damage. Funny/sad. Similar to the chainsaw joke. Anyone remember or have those jokes stored away somewhere that they can drag them out? I didn't think I had any "funny" jokes like the tower joke, etc., but I definitely had some non-fatal "war stories" to tell. I also built a couple of those "repulsion coils" as a kid. Aluminum ring & coat hanger wire core & couple hundred turns of number 14 gauge wire, plug into AC line and the ring would shoot up 1-2 feet. Neat. Playing around with a high turns coil on it one day and didn't realize my fingers were on some terminals and I must have gotten a thousand volts pressed against my thumb: ergo, two burned spots on my thumb. And, that burnt flesh stench. Gawd did it stink. And, it hurt like hell. Radar? I've heard a couple of stories of guys who walked in front of those dishes not knowing they were putting out KWs of microwaves and they got their tummy microwaved into cooked beef. Killed em dead. Better have a buddy around and you can ask him: "Hey, I think this thing is turned off...Am I thinking right? Please go look at all the switches and check, tubes lit up, fans running, hum from transformers, other noises? Please?" Art, W4PON Article: 93619 of rec.radio.amateur.homebrew From: Adrian Brentnall Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power supplies Date: Thu, 14 Jul 2005 12:57:25 +0100 Message-ID: References: <1121288717.540109.24910@g14g2000cwa.googlegroups.com> <11dc65rbamb6qf2@corp.supernews.com> Hi On Thu, 14 Jul 2005 11:45:41 +0000, straydog wrote: > > >On Thu, 14 Jul 2005, Roy Lewallen wrote: > >> Date: Thu, 14 Jul 2005 00:48:01 -0700 >> From: Roy Lewallen >> Newsgroups: rec.radio.amateur.homebrew >> Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power >> supplies >> >> straydog wrote: >>> . . . >>> arcs and smoke can be intimidating. Just the surprise from an arc can make >>> you jump in an unpredictable way and if not hurt yourself from the >>> electrical shock, then you'll bang your head or something else. . . >> >> In a previous life, I was reaching way to the back of a cabinet of radar >> equipment for some reason. I was lying on my stomach, my arm was extended all >> the way, and my head was into the cabinet doorway about at the forehead >> level, with a couple of inches clearance above and below. Of course all the >> safety precautions were followed -- some of the heavy ground radar stuff I >> worked on was easily lethal. But there was some charged capacitor, something >> hot from another cabinet of gear, I don't recall, and I got a minor shock. My >> instinctive reaction was to jerk my head up, and it hit the top of the >> doorway. That hurt and made me reflexively jerk my head downward, hitting the >> bottom of the doorway with my forehead. That caused a jerk back upward, >> hitting the top again, and so forth. There I was, oscillating up and down, >> beating my head to a pulp, knowing exactly what was happening but helpless to >> do anything about it. It continued for what seemed like a long time, until I >> was sore enough that I couldn't feel one more whack, when I was finally able >> to stop and extract my head and arm. I guess I've felt as stupid a few times >> since, but only a few times. >> >> And when you bend your arm every which way in order to get at something, it >> might go in all twisted contorted, but it comes out fast and straight when >> you get bit. I've lost a bit of skin that way, too. >> >> Roy Lewallen, W7EL >> > >Yep. Great story. Reminds me about that sad/funny joke about the guy, his >tower, bucket of tools in a wooden barrel, ropes, pully, and somehow he >goes up and down the tower, wooden barrel breaks so the counterweight >disappears and he goes down again....broken bones, cracked skull, all >kinds of hospital damage. Funny/sad. Similar to the chainsaw joke. Anyone >remember or have those jokes stored away somewhere that they can drag them >out? > That'd be http://monologues.co.uk/004/Bricklayers_Story.htm - at least, that's the original one from Gerard Hoffnung - which dates back a few years. I used to play the tape of this as part of my 'Quality Awareness' sessions - trying to make the point about forward planning, and avoiding situations that are going to cause problems..... There are further versions of this relating to towers and ham radio - a google for Hoffnung + Bricklayer will turn them up Probably funnier to read about than be involved with Take care Adrian Suffolk UK ======return email munged================= take out the papers and the trash to reply Article: 93620 of rec.radio.amateur.homebrew From: Joeseph Subject: What would cause the SWR to go up drastically when I turn my amp on? Date: Thu, 14 Jul 2005 10:31:05 -0400 Message-ID: This is a very screwy problem. First lets get the set-up of my radio equipment; The amp puts out about 100 watts on HF. RADIO----->2 TRANSISTOR AMP----->SWR METER------> ANTENNA Note the SWR meter comes AFTER the 2 transistor amp. Ok, when I check the SWR on my antenna it shows 1.1. When I turn the amp on it shows over 3.x SWR. The antenna is rated at 5 KW. The amp only puts out about 100 watts. Hmmm.....Ok lets see what happens when I use my 1 KW oil filled dummy load. RADIO-----> 2 TRANSISTOR AMP---->SWR METER------->1 KW DUMMY LOAD Same thing. The SWR is about 1.5 in to the dummy load, but as soon as I turn the amp on the SWR meter shows 3.x plus. Ok, Maybe my SWR meter is screwy, so lets use my Dentron MT3000 tuner with a built in 200 watt dry dummy load and built in SWR meter. RADIO ---->2 TRANSISTOR AMP---->DENTRON MT3000 Same thing. The SWR is low without the amp on and goes high when the amp gets turned on. Ok, Lets see what happens when I use my Drake L-4B amp instead of the 2 transistor amp. RADIO----->Drake L-4B----->SWR METER------->Dummy load Now the SWR stays low when I turn on the Drake L-4B for both the 1 KW dummy load and the external antenna. The transistor uses MRF455 transistors. Why would the SWR meter go up significantly when I turn on the 2 transisor amp, but stay low when I turn on a Drake L-4B. I've duplicated this scenario with three different SWR meters, and different patch cables. Lets me say for the record the SWR meter comes after the amp, so I'm not looking at a high SWR on the input side of the amp. This is on the output side of the amp. ????? Article: 93621 of rec.radio.amateur.homebrew From: "Joel Kolstad" Subject: Re: Frequency multipliers: Usable modulation formats? Date: Thu, 14 Jul 2005 08:04:36 -0700 Message-ID: <11dcvl5ao1dsf29@corp.supernews.com> References: <11dabp5hfvvv25@corp.supernews.com> <1121313102.527656.254520@g44g2000cwa.googlegroups.com> Thanks for the detailed reply, Len... I'll sit down and work through some of the math if/when I get a moment. Could you tell which of the following is correct? -- Say I amplitude modulate my voice onto a carrier and feed it through a frequency multiplier. Besides shifting the carrier, does it just make me sound like a chipmunk (i.e., if I manage to hum a perfect 1kHz sine wave, the demodulated signal is me humming a 2kHz sine wave with a 2x mulitplier)? Or is there far more serious distortion present? ---Joel Article: 93622 of rec.radio.amateur.homebrew From: Bill Janssen Subject: Re: What would cause the SWR to go up drastically when I turn my References: Message-ID: <6zvBe.1589$j21.575@news01.roc.ny> Date: Thu, 14 Jul 2005 15:31:14 GMT Joeseph wrote: > > This is a very screwy problem. First lets get the set-up of my >radio equipment; > >The amp puts out about 100 watts on HF. > >RADIO----->2 TRANSISTOR AMP----->SWR METER------> ANTENNA > >Note the SWR meter comes AFTER the 2 transistor amp. > >Ok, when I check the SWR on my antenna it shows 1.1. When I turn the >amp on it shows over 3.x SWR. The antenna is rated at 5 KW. The amp >only puts out about 100 watts. > >Hmmm.....Ok lets see what happens when I use my 1 KW oil filled dummy >load. > > >RADIO-----> 2 TRANSISTOR AMP---->SWR METER------->1 KW DUMMY LOAD > >Same thing. The SWR is about 1.5 in to the dummy load, but as soon as >I turn the amp on the SWR meter shows 3.x plus. > >Ok, Maybe my SWR meter is screwy, so lets use my Dentron MT3000 >tuner with a built in 200 watt dry dummy load and built in SWR meter. > > >RADIO ---->2 TRANSISTOR AMP---->DENTRON MT3000 > >Same thing. The SWR is low without the amp on and goes high when the >amp gets turned on. > > >Ok, Lets see what happens when I use my Drake L-4B amp instead of the >2 transistor amp. > > >RADIO----->Drake L-4B----->SWR METER------->Dummy load > >Now the SWR stays low when I turn on the Drake L-4B for both the 1 KW >dummy load and the external antenna. > >The transistor uses MRF455 transistors. Why would the SWR meter go up >significantly when I turn on the 2 transisor amp, but stay low when I >turn on a Drake L-4B. > >I've duplicated this scenario with three different SWR meters, and >different patch cables. Lets me say for the record the SWR meter >comes after the amp, so I'm not looking at a high SWR on the input >side of the amp. This is on the output side of the amp. > >????? > > > > Check the frequency (or frequencies) coming out of the amplifier. I will bet that what comes out is not equal to what goes in. The antenna is not a good match for those other frequencies. Bill k7NOM Article: 93623 of rec.radio.amateur.homebrew From: "tjs" Subject: MOV protection of 120vac circuits with high freq content Date: Thu, 14 Jul 2005 12:05:22 -0400 Message-ID: <42d69178_1@news1.prserv.net> Not a REC.Radio issue but still appropriate here... Question: will 1-10khz harmonics riding along on 60 hz power cause protective MOVs to charge and short out thusly drawing damaging currents. The scenario: I have an Allen Bradley PLC digital input card and it contains 1 MOV across ac input channel terminals (I think they are MDC Z181 spec). They are there to protect against high voltages at the terminals which I contend never occurs, never seen it happen. What does happens is that a 232 ohm 1/8th watt (current limiting?) resistor just ahead of the MOV will slowly heat up and burn to open circuit in about 30 seconds after connection. Using 0.125W (P=I^2 x R) 232 leads me to exceeding a current of ~25ma drawn to burn the resistor. The IO being monitored is motor run status from a VFD driven motor (variable frequency drive, PWM type, naturally using ~50-100khz synthesis methods). The control power is riddled with harmonics from 500hz to 10khz, and I estimate 10vp-p maybe less (as seen on the oscilloscope). As soon as I close the electrical connector to the IO card the resistors start heating up, smoke, then fail. I know I need to isolate the control power and rid the plc of the harmonics. I just want to confirm the high frequency components can cause MOVs to short as if there was a high voltage event when there isnt one. I beleive the capacitor model of a MOV means it should charge up at higher frequency, and maybe this is why it takes 30 seconds for smoke to appear. Regards Tim KF8XW Article: 93624 of rec.radio.amateur.homebrew From: jk Subject: Re: MOV protection of 120vac circuits with high freq content Message-ID: References: <42d69178_1@news1.prserv.net> Date: Thu, 14 Jul 2005 09:31:40 -0700 "tjs" wrote: >Not a REC.Radio issue but still appropriate here... Well this isn't rec radio either! A mov does not model as a "capacitor" it models as a (verY) non linear resistor. What is the continuous rating of the MOV. >Question: will 1-10khz harmonics riding along on 60 hz power cause >protective MOVs to charge and short out thusly drawing damaging currents. > >The scenario: I have an Allen Bradley PLC digital input card and it contains >1 MOV across ac input channel terminals (I think they are MDC Z181 spec). >They are there to protect against high voltages at the terminals which I >contend never occurs, never seen it happen. What does happens is that a 232 >ohm 1/8th watt (current limiting?) resistor just ahead of the MOV will >slowly heat up and burn to open circuit in about 30 seconds after >connection. Using 0.125W (P=I^2 x R) 232 leads me to exceeding a current >of ~25ma drawn to burn the resistor. > >The IO being monitored is motor run status from a VFD driven motor (variable >frequency drive, PWM type, naturally using ~50-100khz synthesis methods). >The control power is riddled with harmonics from 500hz to 10khz, and I >estimate 10vp-p maybe less (as seen on the oscilloscope). As soon as I >close the electrical connector to the IO card the resistors start heating >up, smoke, then fail. > >I know I need to isolate the control power and rid the plc of the harmonics. >I just want to confirm the high frequency components can cause MOVs to short >as if there was a high voltage event when there isnt one. I beleive the >capacitor model of a MOV means it should charge up at higher frequency, and >maybe this is why it takes 30 seconds for smoke to appear. > >Regards >Tim KF8XW > jk Article: 93625 of rec.radio.amateur.homebrew From: et472@FreeNet.Carleton.CA (Michael Black) Subject: Re: Frequency multipliers: Usable modulation formats? Date: 14 Jul 2005 16:24:15 GMT Message-ID: References: <11dabp5hfvvv25@corp.supernews.com> <1121313102.527656.254520@g44g2000cwa.googlegroups.com> <11dcvl5ao1dsf29@corp.supernews.com> "Joel Kolstad" (JKolstad71HatesSpam@yahoo.com) writes: > Thanks for the detailed reply, Len... I'll sit down and work through some of > the math if/when I get a moment. > > Could you tell which of the following is correct? -- Say I amplitude modulate > my voice onto a carrier and feed it through a frequency multiplier. Besides > shifting the carrier, does it just make me sound like a chipmunk (i.e., if I > manage to hum a perfect 1kHz sine wave, the demodulated signal is me humming a > 2kHz sine wave with a 2x mulitplier)? Or is there far more serious distortion > present? > Virtually all multipliers we see work by overdriving a stage. This strips off any amplitude modulation, so there's no modulation at the output of the multiplier. Michael VE2BVW Article: 93626 of rec.radio.amateur.homebrew From: "Roger Leone" References: <1121290111.687842.193790@g49g2000cwa.googlegroups.com> <1PiBe.2051$_%4.856@newssvr14.news.prodigy.com> <1121334811.401173.310790@g49g2000cwa.googlegroups.com> Subject: Re: QUESTION: Cheap Accurate Shaft Position Encoder Message-ID: Date: Thu, 14 Jul 2005 17:09:33 GMT > Steppers have no output unless the shaft is moving. Steppers used this > way are really a velocity encoder and not a position encoder. > Regards, > Glenn AC7ZN > Glenn: I'm sure that limits stepper motors to certain uses, but I think this thread/post may be incorrectly titled. Unless I misunderstand the intended application, I don't think a "position encoder" is what he is looking for. Rather he wants something that, when rotated, feeds pulses to an up/down counter for frequency synthesis. The position of the shaft is not important as long as its rotation can be used to generate pulses for the counter. Roger Article: 93627 of rec.radio.amateur.homebrew From: Tim Wescott Subject: Re: What would cause the SWR to go up drastically when I turn my Date: Thu, 14 Jul 2005 10:11:52 -0700 Message-ID: <11dd76n2b9qua1d@corp.supernews.com> References: <6zvBe.1589$j21.575@news01.roc.ny> Bill Janssen wrote: > Joeseph wrote: > >> >> This is a very screwy problem. First lets get the set-up of my >> radio equipment; >> >> The amp puts out about 100 watts on HF. >> >> RADIO----->2 TRANSISTOR AMP----->SWR METER------> ANTENNA >> >> Note the SWR meter comes AFTER the 2 transistor amp. >> >> Ok, when I check the SWR on my antenna it shows 1.1. When I turn the >> amp on it shows over 3.x SWR. The antenna is rated at 5 KW. The amp >> only puts out about 100 watts. >> >> Hmmm.....Ok lets see what happens when I use my 1 KW oil filled dummy >> load. >> >> >> RADIO-----> 2 TRANSISTOR AMP---->SWR METER------->1 KW DUMMY LOAD >> >> Same thing. The SWR is about 1.5 in to the dummy load, but as soon as >> I turn the amp on the SWR meter shows 3.x plus. >> >> Ok, Maybe my SWR meter is screwy, so lets use my Dentron MT3000 >> tuner with a built in 200 watt dry dummy load and built in SWR meter. >> >> >> RADIO ---->2 TRANSISTOR AMP---->DENTRON MT3000 >> >> Same thing. The SWR is low without the amp on and goes high when the >> amp gets turned on. >> >> >> Ok, Lets see what happens when I use my Drake L-4B amp instead of the >> 2 transistor amp. >> >> RADIO----->Drake L-4B----->SWR METER------->Dummy load >> >> Now the SWR stays low when I turn on the Drake L-4B for both the 1 KW >> dummy load and the external antenna. >> >> The transistor uses MRF455 transistors. Why would the SWR meter go up >> significantly when I turn on the 2 transisor amp, but stay low when I >> turn on a Drake L-4B. >> >> I've duplicated this scenario with three different SWR meters, and >> different patch cables. Lets me say for the record the SWR meter >> comes after the amp, so I'm not looking at a high SWR on the input >> side of the amp. This is on the output side of the amp. >> ????? >> >> >> >> > Check the frequency (or frequencies) coming out of the amplifier. I will > bet > that what comes out is not equal to what goes in. The antenna is not a > good match for those other frequencies. > > Bill k7NOM What Bill is trying to tell you is that your amplifier is probably oscillating or putting out way bad harmonics. That certainly fits the symptoms with the antenna attached; it's a bit surprising with your dummy load unless the dummy load is only good to two meters (chances are your oscillation is higher than 2M, and harmonics certainly would be). You could also see odd results if the SWR meters aren't good beyond 2M, but I don't know which direction they tend to go with way high frequencies. -- ------------------------------------------- Tim Wescott Wescott Design Services http://www.wescottdesign.com Article: 93628 of rec.radio.amateur.homebrew From: Tim Wescott Subject: Re: Class C amplifier Date: Thu, 14 Jul 2005 10:16:44 -0700 Message-ID: <11dd7fr9bsuoo82@corp.supernews.com> References: <1121320385.670687.309640@g44g2000cwa.googlegroups.com> rkrishnan wrote: > I am reading through the excellent book "Solid State Design" by Wes > Hayward et al. I have a specific question on Class C amplifier. On > chapter 2 Fig 15, a Clas C amplifier is shown with a buffer amplifier > link coupled in front. > > Why is link coupling needed here, can't the collector be directly > connected to the base? It is for impedance matching or is there any > other motives behind this structure? > > 73 > Ramakrishnan, vu3rdd > Any coupling circuit to a class C bipolar transistor amplifier not only needs to match impedance, it also needs to supply DC current to the base of the class C stage. Inductive coupling is nice because the average voltage at the base is nailed at zero and the inductor will guarantee that enough DC current flows. If you should capacitively couple then you need to load the base of the final stage with a back-biased diode or a resistor to provide the current -- otherwise your coupling capacitor will just charge up until no current flows into your final's base and you no longer get amplification. -- ------------------------------------------- Tim Wescott Wescott Design Services http://www.wescottdesign.com Article: 93629 of rec.radio.amateur.homebrew From: Joeseph Subject: Re: What would cause the SWR to go up drastically when I turn my amp on? Date: Thu, 14 Jul 2005 13:17:46 -0400 Message-ID: References: <6zvBe.1589$j21.575@news01.roc.ny> On Thu, 14 Jul 2005 15:31:14 GMT, Bill Janssen wrote: > >> >Check the frequency (or frequencies) coming out of the amplifier. I will bet >that what comes out is not equal to what goes in. The antenna is not a >good match for those other frequencies. > >Bill k7NOM Smart guy you are! I never thought of that, but it makes perfect sense. I don't have a spectrum analyzer, but since the 2nd harmonic and higher lands above 30 MHz then I should be able to place my Barker and Williamson low pass filter (30 MHz cut off) between the amp and the SWR meter. Hopefully the low pass filter will allow the fundamental through, and stop the higher frequencies (assuming they are normal multiples of the fundamental frequency). If the attenuation is great enough the SWR meter should not show the SWR jump since the unwanted frequencies should be attenuated before they get to the SWR meter. Assuming you are correct my next problem will stopping the extra frequencies from getting out of the amp in the first place. J. Article: 93630 of rec.radio.amateur.homebrew From: "big Boss" References: Subject: Re: What would cause the SWR to go up drastically when I turn my amp on? Message-ID: Date: Thu, 14 Jul 2005 17:46:23 GMT Your transistor amp is putting out garbage; transmitting harmonics that your SWR Meter is responding to. You need tuning/lowpass filters on both input and output. "Joeseph" wrote in message news:cpscd1pntms4h0jgucumopkr80r98iotdu@4ax.com... > > > > This is a very screwy problem. First lets get the set-up of my > radio equipment; > > The amp puts out about 100 watts on HF. > > RADIO----->2 TRANSISTOR AMP----->SWR METER------> ANTENNA > > Note the SWR meter comes AFTER the 2 transistor amp. > > Ok, when I check the SWR on my antenna it shows 1.1. When I turn the > amp on it shows over 3.x SWR. The antenna is rated at 5 KW. The amp > only puts out about 100 watts. > > Hmmm.....Ok lets see what happens when I use my 1 KW oil filled dummy > load. > > > RADIO-----> 2 TRANSISTOR AMP---->SWR METER------->1 KW DUMMY LOAD > > Same thing. The SWR is about 1.5 in to the dummy load, but as soon as > I turn the amp on the SWR meter shows 3.x plus. > > Ok, Maybe my SWR meter is screwy, so lets use my Dentron MT3000 > tuner with a built in 200 watt dry dummy load and built in SWR meter. > > > RADIO ---->2 TRANSISTOR AMP---->DENTRON MT3000 > > Same thing. The SWR is low without the amp on and goes high when the > amp gets turned on. > > > Ok, Lets see what happens when I use my Drake L-4B amp instead of the > 2 transistor amp. > > > RADIO----->Drake L-4B----->SWR METER------->Dummy load > > Now the SWR stays low when I turn on the Drake L-4B for both the 1 KW > dummy load and the external antenna. > > The transistor uses MRF455 transistors. Why would the SWR meter go up > significantly when I turn on the 2 transisor amp, but stay low when I > turn on a Drake L-4B. > > I've duplicated this scenario with three different SWR meters, and > different patch cables. Lets me say for the record the SWR meter > comes after the amp, so I'm not looking at a high SWR on the input > side of the amp. This is on the output side of the amp. > > ????? > > Article: 93631 of rec.radio.amateur.homebrew From: Roy Lewallen Subject: Re: What would cause the SWR to go up drastically when I turn my Date: Thu, 14 Jul 2005 10:53:26 -0700 Message-ID: <11dd9ksc9hoeab5@corp.supernews.com> References: <6zvBe.1589$j21.575@news01.roc.ny> Joeseph wrote: > , , , > Assuming you are correct my next problem will stopping the extra > frequencies from getting out of the amp in the first place. No, your problem should be figuring out how to prevent them from getting generated in the first place. If the harmonic or spurious content is that high, there's something seriously wrong. Roy Lewallen, W7EL Article: 93632 of rec.radio.amateur.homebrew From: dplatt@radagast.org (Dave Platt) Subject: Re: What would cause the SWR to go up drastically when I turn my amp on? Date: Thu, 14 Jul 2005 17:56:16 -0000 Message-ID: <11dd9q0s5ok066e@corp.supernews.com> References: >RADIO----->Drake L-4B----->SWR METER------->Dummy load > >Now the SWR stays low when I turn on the Drake L-4B for both the 1 KW >dummy load and the external antenna. > >The transistor uses MRF455 transistors. Why would the SWR meter go up >significantly when I turn on the 2 transisor amp, but stay low when I >turn on a Drake L-4B. If I had to guess, I'd guess that your MRF455 amplifier may have some instability issues, and may have a nasty parasitic oscillation going on. You might also want to check its grounding, and the RF relay which I presume switches it into or out of the circuit. I'm guessing that you've got RF flowing where it shouldn't. I picked up a few MRF455 transistors last year and have toyed with the idea of using them as a PA in a homebrew rig, but from what I can see in the application notes they require a goodly amount of care in the amplifier design and circuit layout. If they aren't used properly it looks to me as if they can be quite prone to misbehave, oscillate, etc. If you can borrow a spectrum analyzer, take a careful look at the amp's output, and wave a probe around the amp itself (prior to the low-pass output filter). It would not surprise me if you find that you're spurring the horse a bit :-) -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! Article: 93633 of rec.radio.amateur.homebrew From: dplatt@radagast.org (Dave Platt) Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power Date: Thu, 14 Jul 2005 18:05:33 -0000 Message-ID: <11ddabdajqbpde1@corp.supernews.com> References: <1121288717.540109.24910@g14g2000cwa.googlegroups.com> In article , Ken Scharf wrote: >I always assumed there was voltage across the caps when I worked on the >rig. First pull the plug(s). Wait till the voltmeter drops to zero. A trick, courtesy of Bob Pease: whenever you build a power supply circuit which carries line voltage or higher, stick an NE-2 neon bulb and a suitable dropping resistor across the caps, and place the bulb where it's clearly visible when the case is opened. If the bulb is lit (at all) the caps have enough voltage in them to give you a nasty bite. >THEN put a heavy screwdriver with a well insulated handle from ground >to the HV terminal to be sure! I've heard cautionary notes about this... if you do this prematurely, the arc can be scary (and dangerous in some cases - "arc flash" burns can be severe) and I believe it's possible to damage or wreck some caps as a side effect of a catastrophic high-current discharge. A heavy grounding wire, with alligator clips, and with a current-limiting resistor is another possible solution. You want a low enough impedance to drain away any charge which may come out of the cap's dielectric "soakage", but high enough to avoid a dangerous arc flash when you first hook it up. > Keep on hand in the pocket if you need to >adjust anything when it's hot. That's one of the best single pieces of advice around! Also, be aware of what sort of grounded metal is around your workbench. Doesn't help much to keep one hand in your pocket, if you lean your belly against a grounded metal bench! > >HV isn't the only thing that can get you. High current can give you >a nasty surprise. Like the guy replacing some batteries on a golf cart. >He was using a ratchet wrench to tighten the battery clamps and he >ended on the most positive battery terminal. The handle of the wrench >hit the chassis of the golf cart putting it between 36 volts and ground >of some VERY HEAVY DUTY batteries. Ever see a Sears ratchet wrench >glow WHITE HOT? (and melt?) Haven't seen that myself, but I've heard of people who have had screwdrivers, etc. literally vaporized under such circumstances. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! Article: 93634 of rec.radio.amateur.homebrew From: "tjs" References: <42d69178_1@news1.prserv.net> Subject: Re: MOV protection of 120vac circuits with high freq content Date: Thu, 14 Jul 2005 14:12:00 -0400 Message-ID: <42d6af25_3@news1.prserv.net> Sorry , I crossposted to rec.radio.amateur.homebrew and sci.eng.electrical sys-protection I'm having trouble finding data on the MOVs. The markings MDC Z181 04UL seem to point to a 175 vac 225vdc 17-19 joule device with 130 pf capacitance, 1200 amps Ipeak, 25mW transient dissipation. I searched Digikey and NTE. It is about 10mm diameter disk type, maybe 8.5mm per some datasheets. Tim "tjs" wrote in message news:42d69178_1@news1.prserv.net... > Not a REC.Radio issue but still appropriate here... > > > Question: will 1-10khz harmonics riding along on 60 hz power cause > protective MOVs to charge and short out thusly drawing damaging currents. > > The scenario: I have an Allen Bradley PLC digital input card and it contains > 1 MOV across ac input channel terminals (I think they are MDC Z181 spec). > They are there to protect against high voltages at the terminals which I > contend never occurs, never seen it happen. What does happens is that a 232 > ohm 1/8th watt (current limiting?) resistor just ahead of the MOV will > slowly heat up and burn to open circuit in about 30 seconds after > connection. Using 0.125W (P=I^2 x R) 232 leads me to exceeding a current > of ~25ma drawn to burn the resistor. > > The IO being monitored is motor run status from a VFD driven motor (variable > frequency drive, PWM type, naturally using ~50-100khz synthesis methods). > The control power is riddled with harmonics from 500hz to 10khz, and I > estimate 10vp-p maybe less (as seen on the oscilloscope). As soon as I > close the electrical connector to the IO card the resistors start heating > up, smoke, then fail. > > I know I need to isolate the control power and rid the plc of the harmonics. > I just want to confirm the high frequency components can cause MOVs to short > as if there was a high voltage event when there isnt one. I beleive the > capacitor model of a MOV means it should charge up at higher frequency, and > maybe this is why it takes 30 seconds for smoke to appear. > > Regards > Tim KF8XW > > Article: 93635 of rec.radio.amateur.homebrew From: Tim Wescott Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power Date: Thu, 14 Jul 2005 11:32:47 -0700 Message-ID: <11ddbuepk3jjr77@corp.supernews.com> References: <1121288717.540109.24910@g14g2000cwa.googlegroups.com> <11ddabdajqbpde1@corp.supernews.com> Dave Platt wrote: > In article , > Ken Scharf wrote: snip >>HV isn't the only thing that can get you. High current can give you >>a nasty surprise. Like the guy replacing some batteries on a golf cart. >>He was using a ratchet wrench to tighten the battery clamps and he >>ended on the most positive battery terminal. The handle of the wrench >>hit the chassis of the golf cart putting it between 36 volts and ground >>of some VERY HEAVY DUTY batteries. Ever see a Sears ratchet wrench >>glow WHITE HOT? (and melt?) > > > Haven't seen that myself, but I've heard of people who have had > screwdrivers, etc. literally vaporized under such circumstances. > My brother came home from a business trip once with a scar on his wrist 5/8 inches wide and all the way around -- the truck was having electrical problems & he shorted his metal watch band through the 12V battery (there was a wrench involved in there somehow, of course). I felt for him, but I was very glad that _he_ was the one to learn this first hand, rather than me... -- ------------------------------------------- Tim Wescott Wescott Design Services http://www.wescottdesign.com Article: 93636 of rec.radio.amateur.homebrew From: Joeseph Subject: Re: What would cause the SWR to go up drastically when I turn my amp on? Date: Thu, 14 Jul 2005 14:50:17 -0400 Message-ID: References: On Thu, 14 Jul 2005 10:31:05 -0400, Joeseph wrote: Thanks for all your help guys. I think you've hit the nail on the head. Now it is time for me to do some more reading, and fix this puppy. J Article: 93637 of rec.radio.amateur.homebrew From: "Mike Andrews" Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power supplies Date: Thu, 14 Jul 2005 18:56:57 +0000 (UTC) Message-ID: References: <1121288717.540109.24910@g14g2000cwa.googlegroups.com> <11ddabdajqbpde1@corp.supernews.com> Dave Platt wrote: > In article , > Ken Scharf wrote: >>HV isn't the only thing that can get you. High current can give you >>a nasty surprise. Like the guy replacing some batteries on a golf cart. >>He was using a ratchet wrench to tighten the battery clamps and he >>ended on the most positive battery terminal. The handle of the wrench >>hit the chassis of the golf cart putting it between 36 volts and ground >>of some VERY HEAVY DUTY batteries. Ever see a Sears ratchet wrench >>glow WHITE HOT? (and melt?) > Haven't seen that myself, but I've heard of people who have had > screwdrivers, etc. literally vaporized under such circumstances. The canonical "Take-Your-Rings-Off" reminder in our electronics shop in Japan, back when I was in the AF, was a color image, taken at our base hospital, of a finger burnt to the bone all the way around: one of the techs had got his wedding ring between ground and a high-current low-voltage supply. -- Mike Andrews W5EGO 5WPM mikea@mikea.ath.cx Extra Tired old sysadmin working on his code speed Article: 93638 of rec.radio.amateur.homebrew From: "tjs" References: <42d69178_1@news1.prserv.net> <42d6af25_3@news1.prserv.net> Subject: Re: MOV protection of 120vac circuits with high freq content Date: Thu, 14 Jul 2005 14:54:33 -0400 Message-ID: <42d6b91e_4@news1.prserv.net> This is close the exact component I have. http://www.maida.com/content/products/varistors/standard/fullRecord.asp?iACVolts=180&iDCVolts=0&iDiskSize=10&stylenum=D6121ZOV181RA04 It shows 320pF. Its marked 04UL is supposed to mean 40 joules, although the data sheet says 60J. Tim I want to conclude that the MOV can short pulling over 25ma thru the 1/8th watt resistor, heating it up, due to 10khz components on the voltage, and not an actual high voltage. Would this be a true statement? Thanks "tjs" wrote in message news:42d6af25_3@news1.prserv.net... > Sorry , I crossposted to rec.radio.amateur.homebrew and sci.eng.electrical > sys-protection > > I'm having trouble finding data on the MOVs. The markings MDC Z181 04UL seem > to point to a 175 vac 225vdc 17-19 joule device with 130 pf capacitance, > 1200 amps Ipeak, 25mW transient dissipation. I searched Digikey and NTE. It > is about 10mm diameter disk type, maybe 8.5mm per some datasheets. > > Tim > > > > "tjs" wrote in message news:42d69178_1@news1.prserv.net... > > Not a REC.Radio issue but still appropriate here... > > > > > > Question: will 1-10khz harmonics riding along on 60 hz power cause > > protective MOVs to charge and short out thusly drawing damaging currents. > > > > The scenario: I have an Allen Bradley PLC digital input card and it > contains > > 1 MOV across ac input channel terminals (I think they are MDC Z181 spec). > > They are there to protect against high voltages at the terminals which I > > contend never occurs, never seen it happen. What does happens is that a > 232 > > ohm 1/8th watt (current limiting?) resistor just ahead of the MOV will > > slowly heat up and burn to open circuit in about 30 seconds after > > connection. Using 0.125W (P=I^2 x R) 232 leads me to exceeding a current > > of ~25ma drawn to burn the resistor. > > > > The IO being monitored is motor run status from a VFD driven motor > (variable > > frequency drive, PWM type, naturally using ~50-100khz synthesis methods). > > The control power is riddled with harmonics from 500hz to 10khz, and I > > estimate 10vp-p maybe less (as seen on the oscilloscope). As soon as I > > close the electrical connector to the IO card the resistors start heating > > up, smoke, then fail. > > > > I know I need to isolate the control power and rid the plc of the > harmonics. > > I just want to confirm the high frequency components can cause MOVs to > short > > as if there was a high voltage event when there isnt one. I beleive the > > capacitor model of a MOV means it should charge up at higher frequency, > and > > maybe this is why it takes 30 seconds for smoke to appear. > > > > Regards > > Tim KF8XW > > > > > > Article: 93639 of rec.radio.amateur.homebrew From: Allodoxaphobia Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power supplies Date: 14 Jul 2005 19:04:03 GMT Message-ID: References: <1121288717.540109.24910@g14g2000cwa.googlegroups.com> <11ddabdajqbpde1@corp.supernews.com> <11ddbuepk3jjr77@corp.supernews.com> On Thu, 14 Jul 2005 11:32:47 -0700, Tim Wescott wrote: > Dave Platt wrote: >> In article , >> Ken Scharf wrote: > snip >>>HV isn't the only thing that can get you. High current can give you >>>a nasty surprise. Like the guy replacing some batteries on a golf cart. >>>He was using a ratchet wrench to tighten the battery clamps and he >>>ended on the most positive battery terminal. The handle of the wrench >>>hit the chassis of the golf cart putting it between 36 volts and ground >>>of some VERY HEAVY DUTY batteries. Ever see a Sears ratchet wrench >>>glow WHITE HOT? (and melt?) >> >> >> Haven't seen that myself, but I've heard of people who have had >> screwdrivers, etc. literally vaporized under such circumstances. >> > My brother came home from a business trip once with a scar on his wrist > 5/8 inches wide and all the way around -- the truck was having > electrical problems & he shorted his metal watch band through the 12V > battery (there was a wrench involved in there somehow, of course). > > I felt for him, but I was very glad that _he_ was the one to learn this > first hand, rather than me... My dad (the first W3DHJ) told me a similar story. It was in the late 20's. He was working on _his_ dad's Ford utility truck. (Grandpa owned a dairy in Big Bear, Calif.) Six volts here. The truck was parked in the driveway -- just outside the garage. When my dad caught his ring between the positive terminal and the truck frame, my Grandpa picked him up bodily -- ran him over to the rain barrel at the corner of the garage -- and stuffed my dad's entire left arm (and much of his upper torso) into the barrel. ( *The worst* thing you could do in a situation like that is try to _pull_ the ring off.) My dad was a 90-day wonder in WW II. He then spent 25+ years in the U.S. Army Corps of Engineers (we traveled the planet....) Most of his duty assignments were as Post Engineer -- with the added responsibity as Post Safety Officer. I always knew him to be evangelically anal about safety. I'm sure that incident with the old Ford truck had a wee bit to do with it. Jonesy -- Marvin L Jones | jonz | W3DHJ | linux Pueblo, Colorado | @ | Jonesy | OS/2 __ 38.24N 104.55W | config.com | DM78rf | SK Article: 93640 of rec.radio.amateur.homebrew Message-ID: <42D6C357.AB6D9035@earthlink.net> From: "Michael A. Terrell" Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV powersupplies References: <1121288717.540109.24910@g14g2000cwa.googlegroups.com> <42D64EAD.9090207@invalid.invalid> Date: Thu, 14 Jul 2005 19:56:25 GMT Doug Smith W9WI wrote: > > Ken Scharf wrote: > > The filter caps were 10 330uf 450v computer grade units in series, each > > Probably dumb (and WAY off topic) question: > > What's the *intended* purpose of a 450v "computer grade" capacitor? > > -- > Doug Smith W9WI > Pleasant View (Nashville), TN EM66 > http://www.w9wi.com They were used on the input side of large switching supplies for minicomputers, and some later mainframes. I pulled about 100 of them >from the multiple switching supplies in an Amdal mainframe about 10 or 12 years ago. -- Link to my "Computers for disabled Veterans" project website deleted after threats were telephoned to my church. Michael A. Terrell Central Florida Article: 93641 of rec.radio.amateur.homebrew From: Roy Lewallen Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power Date: Thu, 14 Jul 2005 13:27:57 -0700 Message-ID: <11ddimdf7ssksb4@corp.supernews.com> References: <1121288717.540109.24910@g14g2000cwa.googlegroups.com> <11ddabdajqbpde1@corp.supernews.com> Don't forget about "soak", also known as dielectric absorption or dielectric hysteresis. In some capacitors, particularly electrolytics, charge "soaks" into the dielectric and can take from seconds to days to work its way out. The result is a "discharged" capacitor that seems to spontaneously recharge itself. (One story I heard during my broadcast days was someone who put a screwdriver across a "discharged" capacitor. After he picked himself up off the floor, he found just the handle of the screwdriver. He was lucky his eyes weren't hit with molten metal. You'll often find large capacitors stored with a shorting wire across them -- a good idea.) I recommend leaving a heavy cliplead in place across the high voltage capacitors for the entire time you're working on the unit. Put some tape over the on/off switch and/or a tag on the plug to remind you to remove it before turning the power back on. As a side note, the aquadag coating of a CRT is notorious for this. I've gotten a healthy bite off a CRT the day after it was discharged for an hour or more with a cliplead. Roy Lewallen, W7EL Article: 93642 of rec.radio.amateur.homebrew From: Roy Lewallen Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power Date: Thu, 14 Jul 2005 13:30:20 -0700 Message-ID: <11ddiqsnpp42r5f@corp.supernews.com> References: <1121288717.540109.24910@g14g2000cwa.googlegroups.com> <11ddabdajqbpde1@corp.supernews.com> Mike Andrews wrote: > > The canonical "Take-Your-Rings-Off" reminder in our electronics shop > in Japan, back when I was in the AF, was a color image, taken at our > base hospital, of a finger burnt to the bone all the way around: one of > the techs had got his wedding ring between ground and a high-current > low-voltage supply. What we got was a nice photograph of a finger in a dish with the ring, right beside the newly customized hand. Roy Lewallen, W7EL Article: 93643 of rec.radio.amateur.homebrew From: Tim Wescott Subject: Re: Frequency multipliers: Usable modulation formats? Date: Thu, 14 Jul 2005 14:40:01 -0700 Message-ID: <11ddmtfrscao0f5@corp.supernews.com> References: <11dabp5hfvvv25@corp.supernews.com> <1121313102.527656.254520@g44g2000cwa.googlegroups.com> <11dcvl5ao1dsf29@corp.supernews.com> <1121376604.674866.94510@g49g2000cwa.googlegroups.com> Mark wrote: > and it will NOT work with QPSK > > Mark > It would work to the extent that if you go 4x you could phase lock for a reference -- but you wouldn't have QPSK any more. -- ------------------------------------------- Tim Wescott Wescott Design Services http://www.wescottdesign.com Article: 93644 of rec.radio.amateur.homebrew From: straydog Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power Date: Fri, 15 Jul 2005 00:31:53 +0000 Message-ID: References: <1121288717.540109.24910@g14g2000cwa.googlegroups.com> On Thu, 14 Jul 2005, Tim Wescott wrote: > Date: Thu, 14 Jul 2005 11:32:47 -0700 > From: Tim Wescott > Newsgroups: rec.radio.amateur.homebrew > Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power > supplies > > Dave Platt wrote: >> In article , >> Ken Scharf wrote: > snip >>> HV isn't the only thing that can get you. High current can give you >>> a nasty surprise. Like the guy replacing some batteries on a golf cart. >>> He was using a ratchet wrench to tighten the battery clamps and he >>> ended on the most positive battery terminal. The handle of the wrench hit >>> the chassis of the golf cart putting it between 36 volts and ground >>> of some VERY HEAVY DUTY batteries. Ever see a Sears ratchet wrench >>> glow WHITE HOT? (and melt?) >> >> >> Haven't seen that myself, but I've heard of people who have had >> screwdrivers, etc. literally vaporized under such circumstances. >> > My brother came home from a business trip once with a scar on his wrist 5/8 > inches wide and all the way around -- the truck was having electrical > problems & he shorted his metal watch band through the 12V battery (there was > a wrench involved in there somehow, of course). > > I felt for him, but I was very glad that _he_ was the one to learn this first > hand, rather than me... I've got a related story to tell: I saw many years ago two guys try to jump start another guy in the winter time. I only saw a few seconds and surmised the following. These guys must have used the jumper cables to connect the two twelve volt batteries in series, not parallel. Why? The jumper cables were, themselves, literally smoking and not just a little bit. Figure 24 volt power at, what, something like 500 amps(?) split between heating up the interior of the two batteries and those jumper cables (that are usually like #4 or #6 gauge?). How many seconds would it take for on the order of 5000 watts to cause jumper cables to get up to 200-300+ degrees Farenheit? Those guys scrambled to tear those cables off the batteries and I could tell by how they were handling the cable that it had to be hot. They could have warped the lead plates. > -- > ------------------------------------------- > Tim Wescott > Wescott Design Services > http://www.wescottdesign.com > Article: 93645 of rec.radio.amateur.homebrew From: straydog Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power Date: Fri, 15 Jul 2005 00:38:10 +0000 Message-ID: References: <1121288717.540109.24910@g14g2000cwa.googlegroups.com> On Thu, 14 Jul 2005, Roy Lewallen wrote: > Date: Thu, 14 Jul 2005 13:27:57 -0700 > From: Roy Lewallen > Newsgroups: rec.radio.amateur.homebrew > Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power > supplies > > Don't forget about "soak", also known as dielectric absorption or dielectric > hysteresis. In some capacitors, particularly electrolytics, charge "soaks" > into the dielectric and can take from seconds to days to work its way out. > The result is a "discharged" capacitor that seems to spontaneously recharge > itself. (One story I heard during my broadcast days was someone who put a > screwdriver across a "discharged" capacitor. Yep, I can vouch for this effect. I've seen it, too. Short the cap with alligator clip-tipped wire for a few seconds if you want that voltage down to microvolts. I think it is not "soak" but simple RC time constant decay. Just like radioactive half-life. Residual voltage on a cap _never_ goes to true zero, only according to the decay equation. However, there is a so-called "electret" effect which really sounds like your "soak" effect. After he picked himself up off > the floor, he found just the handle of the screwdriver. He was lucky his eyes > weren't hit with molten metal. You'll often find large capacitors stored with > a shorting wire across them -- a good idea.) D'arsonval meters, especially sensitive ones, are also best stored with a shorting wire accross the terminals. I recommend leaving a heavy > cliplead in place across the high voltage capacitors for the entire time > you're working on the unit. Put some tape over the on/off switch and/or a tag > on the plug to remind you to remove it before turning the power back on. > > As a side note, the aquadag coating of a CRT is notorious for this. I've > gotten a healthy bite off a CRT the day after it was discharged for an hour > or more with a cliplead. > > Roy Lewallen, W7EL > Article: 93646 of rec.radio.amateur.homebrew From: straydog Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power Date: Fri, 15 Jul 2005 00:48:50 +0000 Message-ID: References: <1121288717.540109.24910@g14g2000cwa.googlegroups.com> I forgot to tell my "parasitic" story..see below... On Wed, 13 Jul 2005 Timothy@tholtom.freeserve.co.uk wrote: > Date: 13 Jul 2005 14:05:17 -0700 > From: Timothy@tholtom.freeserve.co.uk > Newsgroups: rec.radio.amateur.homebrew > Subject: QUESTION: Fun with Svetlanas or Staying alive with kV power supplies > > My knowledge of vacuum tubes and kV power supplies is limited. I have > been reading an article in the ARRL Handbook detailing the construction > of a 1kW HF Linear. I'd like to try my hand at building something like > this. I found the article a little intimidating: Ceramic insulators, > parasitic suppressors, thermal and mechanical engineering etc. Is > there some book that details this type of thing with an explanation of > the whys as well as the whats and hows. My priorities are: > > 1) Safety. I'd like to be alive to make my first 1kW QSO > 2) Avoiding equipment destruction, arc overs, black smoke, explosions > etc > 3) Safetly troubleshooting this kind of equipment, loading testing > etc. > 4) How to deal with tubes: warm up, care, etc... > 5) Avoiding TVI (ITV), parasitic oscillations etc. I built this two 811-a linear amplifier way long ago. Basically ave power 300 watts DC input. So, I made my own parasitic suppressors (turns of wire over, say, a ten ohm two watt carbon resistor. Or adjust turns). This was for a 75 meter phone band. So, on launch day it sits there like a scared bird. Turn on fil power, plate power (this is grounded-grid for stability and minimal if not zero need for neutralizations), and tune (no drive) the plate capacitor. Result: dang, RF output through the power meter AND smoke comes out the top of the amp and I stand up, look down, and the coils of wire (made of #22 or 24 gauge wire, can't remember) around the resistors are glowing red hot! Too many turns of wire, so next time around I cut back to half and all was OK. Including no self-oscillation in the two 811-As. That's called trial and error. Or, try, smoke, fix. Like if ready, fire, aim does not work, change the order to ready, aim, fire. Art, W4PON > 6) Longevity and Duty Cycle issues etc. > 7) Costs and sources. > > Hope someone can help. > > Thanks, > > Tim > > Article: 93648 of rec.radio.amateur.homebrew Date: Thu, 14 Jul 2005 21:18:21 -0400 From: -ex- Subject: Re: TAKE A MINUTE EVERYONE References: Message-ID: <4f494$42d70ee0$4232bd6a$14940@COQUI.NET> Edward Pereira wrote: > Basic Facts A while back, I was browsing these newsgroups, just like you > are now, and came across an article similar to this that said you could > make thousands of CASH within weeks with only an initial investment of > $6.00 plus stamps! > So I thought, "Yeah, right, this must be a scam!" Smart guy. -BM Article: 93649 of rec.radio.amateur.homebrew From: et472@FreeNet.Carleton.CA (Michael Black) Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV powersupplies Date: 15 Jul 2005 02:04:59 GMT Message-ID: References: <1121288717.540109.24910@g14g2000cwa.googlegroups.com> <42D64EAD.9090207@invalid.invalid> <42D6C357.AB6D9035@earthlink.net> "Highland Ham" (abcgm0csz.kn6whxyz@dsl.pipex.com) writes: >>> What's the *intended* purpose of a 450v "computer grade" capacitor? > ==================== > Switch mode power suppplies ?? > > > Frank GM0CSZ / KN6WH > > I thought "computer grade" was either a marketing name, or at the very most defined a certain design of capacitor. In other words, they weren't designed for computers, but saw a lot of use in them. They weren't cheap electrolytics of the type you'd see in the average consumer equipment of thirty years ago. You'd see them promoted in the surplus ads, and the ones I remember were metal-cased, and had screw terminals for connections. I still have one around I bought at a hamfest for a 12V power supply. It was about 10,000uF (which was a fairly large size capacitor circa 1973 or so), had a voltage rating of about 16volts, and was the size of a can of coke. Obviously a lot more impressive than the average electrolytic of the day. So once you had that style, it wasn't whether they were used in computers or not, so of course you could have high voltage "computer grade" capacitors. I have no idea if it was a marketing ploy, "hey those are used in computers [which were still uncommon at the time, and usually big and very expensive], they must be good capacitors", or if there was something about their design that made them better than the average electrolytic of the time. Michael VE2BVW Article: 93650 of rec.radio.amateur.homebrew Date: Thu, 14 Jul 2005 22:40:07 -0400 From: -ex- Subject: Re: Simple questions on receivers References: <1121199166.494373.59190@g49g2000cwa.googlegroups.com> <11d8bpfoa35o6c3@corp.supernews.com> <1121392518.226007.109060@g44g2000cwa.googlegroups.com> Message-ID: <6ff44$42d7220c$4232bd6a$2073@COQUI.NET> dave.harper wrote: > Joel Kolstad wrote: > > >>No, although for low Q resonators, it's often pretty close. >> >>Generally speaking, most relatively simple AM receivers are really only >>intended to pick up relatively strong, nearby transmitters. As such, you can >>get away with an awful lot of "cut and try" when it comes to designing the >>circuit (largely ignore matching impedances, Q's, etc.) and still obtain >>acceptable results. > > > Thanks for the response Joel. So if I understand correctly, Q is > basically an indicator of how well the LC circuit resonates? Could you > think of Q as the inverse of a dampening coefficient? > > If so, I guess ideally you'd get the best Q with an iron-core inductor, > thick windings, and as few windings as possible? > > Dave > If I may jump in.... The case of crystal receivers is somewhat different than a "powered" radio in that you want to keep things at as high a Q as possible to match the high impedance of the circuit. High Q is desirable in any case but moreso in a crystal set. After having established a good high Q with the LC configuration you can count on the circuit/antenna loading it down somewhat so then it becomes a matter of selecting appropriate diodes, decoupling the ant, etc. so it always helps to start out with as much as possible. Textbook Q of more C/less L is dictated simply by resistance. In practice, at least for BCB xtal radios, the dielectric of the coil, skin effects of the wire, interwinding capacitance are the key players. Thats why certain coil dimensions, use of litz wire and certain winding techniques can generally be counted on for the highest Q. The Q of a coil, and/or complete circuit, will have a curve of its own. With BCB, what is good at 600kc may be better at 800kc and (relatively) terrible at 1600kc. I've had good success with ferrite toroids approaching Q=400, although ferrites are by nature very unpredictable Q-wise. This is as good as one can expect with something like a 3-4" diameter coil of #18 wire on a good coil form. OTOH, the toroid stops there. That same 4" coil wound with 660-strand litz can get up into the Q=800 stratosphere with a basket-wind technique. There's always a downside. A big, hi-Q coil needs to be kept well away >from ANYTHING or else the Q will take a nosedive and then lead capacitance starts biting you from the backside. I find xtal sets fascinating. I've been radioing for 35-40 years and never gained a full appreciation for L, C and Q until I got into DXing with xtal sets. Logged 105 BCB stations in the competition earlier this year including two in Brazil! -Bill Article: 93651 of rec.radio.amateur.homebrew From: Roy Lewallen Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power Date: Thu, 14 Jul 2005 19:47:23 -0700 Message-ID: <11de8ts392ut099@corp.supernews.com> References: <1121288717.540109.24910@g14g2000cwa.googlegroups.com> <11ddabdajqbpde1@corp.supernews.com> <11ddimdf7ssksb4@corp.supernews.com> straydog wrote: > > Yep, I can vouch for this effect. I've seen it, too. Short the cap with > alligator clip-tipped wire for a few seconds if you want that voltage > down to microvolts. I think it is not "soak" but simple RC time constant > decay. Just like radioactive half-life. Residual voltage on a cap > _never_ goes to true zero, only according to the decay equation. > However, there is a so-called "electret" effect which really sounds like > your "soak" effect. No, it's not a simple time constant -- the slope is much different. A reasonably good model of it is a series R, shunt C, series R, shunt C, etc. A large number of Rs and Cs with various time constants have to be used to imitate it reasonably well. I don't know about an "electret effect". An electret is a dielectric with a permanently trapped charge, so it produces a static electric field. It's the analog of a magnet, with permanently trapped flux and producing a permanent magnetic field. A magnet that's not moving can't produce a current (much to the dismay of the perpetual motion crowd), and an electret that's not moving can't produce a voltage. > > D'arsonval meters, especially sensitive ones, are also best stored with > a shorting wire accross the terminals. That's for an entirely different reason -- to protect the meter from damage, rather than the user. Roy Lewallen, W7EL Article: 93652 of rec.radio.amateur.homebrew From: Roy Lewallen Subject: Re: Simple questions on receivers Date: Thu, 14 Jul 2005 22:00:29 -0700 Message-ID: <11degne6dprob29@corp.supernews.com> References: <1121199166.494373.59190@g49g2000cwa.googlegroups.com> <11d8bpfoa35o6c3@corp.supernews.com> <1121392518.226007.109060@g44g2000cwa.googlegroups.com> dave.harper wrote: > > Thanks for the response Joel. So if I understand correctly, Q is > basically an indicator of how well the LC circuit resonates? Could you > think of Q as the inverse of a dampening coefficient? Just about exactly. You'll find the term "damping factor" (sometimes "damping ratio" or "damping coefficient") often used in many situations involving network analysis and control systems, usually represented by the lowercase Greek letter zeta. And it's numerically equal to 1/(2Q), so Q is exactly 1/2 the inverse of the damping factor. When the damping factor is 1 (Q = 0.5), a second order circuit is said to be critically damped. Roy Lewallen, W7EL Article: 93653 of rec.radio.amateur.homebrew Date: Fri, 15 Jul 2005 01:42:56 -0400 From: -ex- Subject: Re: Simple questions on receivers References: <1121199166.494373.59190@g49g2000cwa.googlegroups.com> <1121402521.763416.59680@z14g2000cwz.googlegroups.com> Message-ID: <3ab17$42d74ce4$4232bd6a$15556@COQUI.NET> LenAnderson@ieee.org wrote: Before I start my rant, let me excuse myself to Len (who I highly regard) for taking some issues to point on the actually-having-done-it level. > > > "Gain" of a crystal radio depends on the bigness of the antenna. > > If you are talking about a loop antenna on an AM [BC band] > radio, then it's a different story. The loop antenna on an > AM receiver is small/tiny/micro-stuff relative to the 200+ > meters of AM BC wavelengths. The received signal VOLTAGE > is directly dependent on the number of turns in that loop and > the physical size of the loop. Loop antennas do suck on a xtal set for that reason but "bigness" can suck equally if not done right. > > > A humungous-long wire is going to supply the greatest amount of > POWER to a crystal receiver. POWER drives the headphones. But, > the amount of power coupled in involves IMPEDANCE and that, right > away, gets into a complicated mess of more electrical rules. You know how you read all those old texts about using nice glass insulators and keeping the wire away from anything? In everyday practice you can do pretty well what you please with wire antennas and powered radios and notice very little difference. Once you get into the realm of truly hi-z installations those tree leaves brushing against the wire become noticeable. > > Simple crystal receivers want to keep impedances very high at > both input, middle, and output. ["crystal" or piezo-electric > headphones are the best for that, next best is the highest > impedance magnetic headphones (2000 Ohms or higher) you can get] Acutally the best is a good matching xfmr and sound powered phones. Those old 1920's 2k headsets are relatively deaf. But you did specify "simple crystal receivers" and it that case it doesn't really matter. > > For the typical parallel-tuned L-C input to a crystal set, the > inductor Q will make a difference. It must be as high as is > practical; Qs of 200 to 300 have been done. But, the Q of the > coil is dependent on a LOT of different factors which I noted > in the other message. Q in excess of 1000 is readily achievable. 200-300 is a starting point on a decent dx set. > > > >>How come the coils on many of the CR schematics > > > Mostly, that is just old-time tradition! :-) [I kid you not] > > The formula for resonance is: F^2 = 1 / (39.478 * L * C) ....snipping here.... > The maximum to minimum variable capacitance ratio is equal to > the square of the maximum to minimum frequency tuning ratio > desired. That's about IT. Most of these old ckts relied on a 17 or 21 plate cap which was in the 400-500 pf range. They would tune the entire band at full tapping. The tapping allowed a guy to really nitpick his tuning for two reasons...ease of fine tuning and higher Q at the best combination. > > "Taps" on a coil can be to select different inductance values > for resonance with limited-range variable tuning capacitors. > Note: Back in the prehistory of radio, like around the 1920s, > variable capacitors were expensive and not so easy to get. A > few old-time crystal sets "tuned" via lots of coil taps using > a fixed parallel capacitor. I had a Philmore crystal radio kit > back in 1946 that did that. Very cheap kit. It worked, so-so. I think you described the Philmore kit well. That was a toy. My 4 cents worth. -Bill Article: 93654 of rec.radio.amateur.homebrew From: Paul Keinanen Subject: Re: QUESTION: Spectrally pure DDS Output? Message-ID: References: <1121289520.683685.321330@o13g2000cwo.googlegroups.com> Date: Fri, 15 Jul 2005 10:24:55 +0300 On Fri, 15 Jul 2005 04:52:57 GMT, charlesh3@msn.com wrote: >I think you'll have to say what is acceptable to you and define what you >mean by "spectral grass". In terms of phase noise, you'll do better with a >normally designed DDS than you will with a normally defined PLL. For data on >what a DDS can do rephase noise, look at various models of synthesizers on >the PTS web site. > >Now of course there are spurs to contend with in any DDS design, but >discrete spurs are not what I would call "spectral grass". If spurs are >indeed your issue, you can go to a 14 bit DDS (AD9951 or others) and get at >least spurs at least 80 db down, or add filtering to the DDS output. The total spur power seems to be more or less constant in the traditional DDS. However the distribution of the spur power varies constantly with the frequency (i.e. phase accumulator increment). At some settings there will be a huge number of low level spurs more or less evenly distributed along the frequency band. I assume that the OP is calling this spectral grass. However, at some specific phase accumulator increments, the spur power is concentrated on just a few discrete frequencies, adding up to easily visible spur peaks, but between these peaks the spectrum is clean (only thermal noise). If the discrete spurs cause problems, it would be a good idea to check if the frequency management could be modified in such a way that the spot frequencies that cause large discrete spurs are skipped. OTOH, if a very clean signal is required in a narrow band, it might be a good idea to concentrate the total spur power into a few discrete spurs outside the band and thus have a clean band of interest. Paul OH3LWR Article: 93655 of rec.radio.amateur.homebrew From: "tjs" References: <42d69178_1@news1.prserv.net> <42d6af25_3@news1.prserv.net> <42d6b91e_4@news1.prserv.net> Subject: Re: MOV protection of 120vac circuits with high freq content Date: Fri, 15 Jul 2005 07:59:25 -0400 Message-ID: <42d7a952_3@news1.prserv.net> Yes I think I will have to test the MOVs to really know. Or as you suggested take a MOV out and measure resistor temperature. "John Popelish" wrote in message news:g7Sdnbgh8tnnIUvfRVn-tg@adelphia.com... > tjs wrote: > > This is close the exact component I have. > > http://www.maida.com/content/products/varistors/standard/fullRecord.asp?iACVolts=180&iDCVolts=0&iDiskSize=10&stylenum=D6121ZOV181RA04 > > It shows 320pF. Its marked 04UL is supposed to mean 40 joules, although the > > data sheet says 60J. > > Tim > > > > I want to conclude that the MOV can short pulling over 25ma thru the 1/8th > > watt resistor, heating it up, due to 10khz components on the voltage, and > > not an actual high voltage. Would this be a true statement? > > Without having the exact waveform, it is impossible to say exactly how > much current the MOV capacitance allows through. I suggest you try an > experiment of removing one of the MOVs and see how much cooler the > resistor runs. Article: 93656 of rec.radio.amateur.homebrew From: "Dale Parfitt" References: Subject: Re: What would cause the SWR to go up drastically when I turn my amp on? Message-ID: Date: Fri, 15 Jul 2005 12:44:13 GMT > Thanks for all your help guys. I think you've hit the nail on the > head. Now it is time for me to do some more reading, and fix this > puppy. > > J > > I have not seen much description on the solid state amp except that it has MRF455 transistors. Because these devices were a favorite in the manufacture of CB amplifiers, I am suspicious that the only output filtering is a HPF set to cutoff around 30MHz. So, running this amp on the lower HF bands would allow a lot of harmonic energy to appear at the output. Dale W4OP Article: 93657 of rec.radio.amateur.homebrew From: "Derek Twynham" Subject: Re: What would cause the SWR to go up drastically when I turn my amp on? Date: Fri, 15 Jul 2005 14:46:39 +0200 Message-ID: References: > RADIO----->2 TRANSISTOR AMP----->SWR METER------> ANTENNA > > Ok, when I check the SWR on my antenna it shows 1.1. When I turn the > amp on it shows over 3.x SWR. The antenna is rated at 5 KW. The amp > only puts out about 100 watts. When I had this it was caused by arcing at the antenna. VSWR perfect with low power, but it even made an audible noise when you screwed the power up. 1 - Try this using a band-pass filter: RADIO-->2 TRANSISTOR AMP-->SWR METER-->FILTER-->DUMMY If amp churns out shit then the filter will reflect it. If VSWR is good, then: 2 - Eliminate your feeder (could be breaking down): RADIO-->2 TRANSISTOR AMP-->SWR METER-->FEEDER-->DUMMY When you do this you may even see a duff contact/joint. If the feeder insulation is breaking down then VSWR rises again. If not then: 3 - Check out the antenna / balun / feed points for strands of wire, smoke, etc. Article: 93658 of rec.radio.amateur.homebrew From: "Derek Twynham" Subject: Re: Murata Ceramic Filters Date: Fri, 15 Jul 2005 14:52:45 +0200 Message-ID: References: > Does anyone know of a retail vendor that would sell the Murata ceramic > filter CFJ455K5 without a $25-$5000 minimum order? http://www.barendh.com has: CFWM450I 4 12 455 Rather steep filter on 450kHz! 9.90 CFK455J 2.7 6 455 17x7 steil ssb 36.50 CFK455E 15 20 455 17x7 very steep 19.90 CFS455E 15 30 455 28x11 Steep filter 32.50 CFS455H 6 13 455 28x11 Steep filter 32.50 CFS455J 2.7 6 455 28x11 Steep filter 35.00 CFL455DG2 20 40 455 16x7 extremely flat group delay 36.26 CFR455G 12 22 455 7x22 Very steep 19.95 LFD15 15 25 455 28x11 Very steep 44.92 CFM455... several bandwidths stocked CFM455H 6 15 455 ***STEEP- METAL CAN- SPEC.OFFER *** 5.67 CFM455A 35 70 455 7x22 Meteosat 31.31 CFG455F 12 25 455 7x11 Narrowband FM 26.77 CFG455I 4 9 455 7x11 Narrow AM 29.00 (prices in Euros) Article: 93659 of rec.radio.amateur.homebrew From: "Derek Twynham" Subject: Re: How do you measure impedance a broadband transformer? Date: Fri, 15 Jul 2005 15:13:11 +0200 Message-ID: References: <42c73578.200999@news.verizon.net> > How do you measure the impedance of a broadband transformer for a RF > transistor amplifier? I'm referring to the input and output broadband > tranformers just before and after the transistor finals. You don't! The broadband transformer reflects the load impedance back to the driving stage. In other words, if the turns-ratio is 1:1 then the input impedance of the transformer is equal to the load impedance. If your load is 50 Ohms and you want to match a 10-watt transmitter, with a 12v supply, then you need to calculate the impedance ratio. The transmitter output stage impedance (in Ohms) is (Vsupply squared) / Watts With 12 v supply, the output impedance of a 10- watt amplifier is (12 x 12) / 10 = 144 / 10 = 14.4 Ohms. The transformer impedance ratio is therefore: 14.4 : 50 = 1 : 3.5 The transformer turns ratio is therefore Sqrt ( impedance ratio) = 1: 1.8 (close enough to 1:2) step-up. Article: 93660 of rec.radio.amateur.homebrew From: tim gorman Subject: Re: Why does a change in jumper length change amplifer outout? References: <8cv8d11adq3khsi653abthf78u126399ta@4ax.com> <3b12bd.52j.ln@tg6124.ab0wr.net> <11d96oksfgpfa03@corp.supernews.com> Message-ID: Date: Fri, 15 Jul 2005 11:57:45 -0500 Roy Lewallen wrote: > > > tim gorman wrote: >> . . . >> Unless you are using rg174 the 7 foot of extra cable should not make this >> much difference unless the input impedance of the amplifer is not 50ohm >> resistive. If it is not purely resistive then changing the cable length >> can impact the SWR seen at the transmitter end significantly. . . > > Changing the cable length won't change the SWR on the cable regardless > of the kind of load impedance and, if the SWR meter is designed for the > cable's Z0, it won't change the SWR meter reading, either. Except, of > course, that cable loss will always lower the SWR -- but that shouldn't > be a significant factor with such short cables. > > Changing the cable length *will* change the impedance looking into the > cable, whether or not the load is purely resistive. The only exception > to this is if the load is resistive *and equal to the line's > characteristic impedance* in which case the impedance looking in will be > Z0 for any length cable. > > > Roy Lewallen, W7EL I repeat, changing the cable length will change the swr *seen* at the transmitter end significantly. As w7el says, changing the cable length will change the impedance looking into the cable. Since most common, inexpensive swr meters are calibrated for use with a 50ohm load, the actual swr readings will be dependent upon the impedance presented to the swr meter while looking into the cable. Although the actual swr may not change, the swr that you see may very well change. A 7 foot stub represents an eighth wavelength all the way down to 60m. This is enough to present an impedance change. tim ab0wr Article: 93661 of rec.radio.amateur.homebrew From: "Heytubeguy" Subject: FA:'S' Mmeters for HQ-110,Sx-42 + more stuff Message-ID: <2kSBe.423748$cg1.332150@bgtnsc04-news.ops.worldnet.att.net> Date: Fri, 15 Jul 2005 17:25:18 GMT Nice 'S' meters for HQ-110 AND SX-42 + other stuff being added; see at: http://search.ebay.com/_W0QQfgtpZ1QQfrppZ25QQsassZheytubeguy Tnx for looking , Heytubeguy Article: 93662 of rec.radio.amateur.homebrew From: "Reg Edwards" Subject: Re: What would cause the SWR to go up drastically when I turn my amp on? Date: Fri, 15 Jul 2005 19:12:06 +0000 (UTC) Message-ID: References: To think in terms of SWR readings is a waste of time and effort. You are all confusing yourselves. Furiously digging yourselves even further into the mire. Go back to square one and begin again from Ohm's Law. ---- Reg Article: 93663 of rec.radio.amateur.homebrew From: straydog Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power Date: Fri, 15 Jul 2005 19:26:00 +0000 Message-ID: References: <1121288717.540109.24910@g14g2000cwa.googlegroups.com> On Fri, 14 Jul 2005 LenAnderson@ieee.org wrote: > Date: 14 Jul 2005 20:48:16 -0700 > From: LenAnderson@ieee.org > Newsgroups: rec.radio.amateur.homebrew > Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power > supplies > > From: straydog on Fri 15 Jul 2005 00:48 > > >> That's called trial and error. Or, try, smoke, fix. Like if ready, fire, >> aim does not work, change the order to ready, aim, fire. > > All electronics works on smoke. If the smoke leaks out, > it won't work... > ;-) Reminds me of another joke I can't quite remember: something dealing with the proof that electricity is really smoke, or something like that. Maybe someone has a reference to that joke. It was pretty funny, too. Art, W4PON > > LenAnderson@ieee.org > > Article: 93664 of rec.radio.amateur.homebrew Subject: ** FLEA at MIT ** Sunday July 17th Cambridge MA From: w1gsl@mit.edu (Steven L. Finberg) Date: 15 Jul 2005 19:39:02 GMT Message-ID: <42d810d6$0$569$b45e6eb0@senator-bedfellow.mit.edu> This coming Sunday.... +++ Now even more Buyers Parking !!! Thanks to TKT we have use of their new parking lot across Albany St from the SWAPFEST !!! !! ** More Buyers PARKING is available ** for details see http://web.mit.edu/w1gsl/Public/flyer *** !!!! In our Traditional GARAGE and the adjacent lot !!!! **** so come rain or shine or super heat the Flea is on !!! ********* $1 buyers discount with hardcopy of this notice ******** COMPUTERS - ELECTRONICS - HAM RADIO - COMPUTERS - ELECTRONICS - HAM RADIO FLEA all SUMMER at MIT Sunday July 17th 2005 9AM-2PM Come to the city for a great flea - plenty of free parking. MIT's electronics and ham radio flea will take place on the third Sunday of each month this summer, April thru October. There is tailgate space for over 600 sellers and free, off-street parking for >2000 cars! Buyers admission is $5 (you get $1 off if you're lucky enough to have a copy of our ad) and sellers spaces are $20 for the first and $15 for each additional at the gate. The flea will be held at the corner of Albany and Main streets in Cambridge; right in the Kendall Square area from 9AM to 2PM, with sellers set-up time starting at 7AM. SEASON PASS + Advance Seller Discount A sellers discount season pass is available which offers a 30% discount. By prepaying you get a discount and earlier admission. See the registration form. *** Attention Sellers *** Prepaid vendors.. Season Pass or monthly, will be admitted FIRST. Separate lines will form prior to gate opening for prepaid and nonprepaid vendors !! RAIN or SHINE !! Have no fear of rain, a covered well illuminated tailgate area is available for all sellers (6'8" clearance). Talk-in: 145.23- (PL 88.5) W1BOS/R and W1XM/R-449.725/444.725 (PL 114.8/2A). Sponsors: MIT Electronics Research Society MIT UHF Repeater Association (W1XM) MIT Radio Society (W1MX) Harvard Wireless Club (W1AF) For more info / advanced reservations 617 253 3776 ********** $1 buyers discount with hard copy of this notice ************ <<<<<<<<<<<<<<<<<<<<<<<< cut here >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Mail the coupon below by the 5th of the month to be a Prepaid Vendor. FLEA at MIT 2005 Rates SELLERS To use your prepaid spaces the named vendor MUST be present. Rates include one admission per space. Advance $17 First space - includes $10 Cambridge Vendor License $12 Additional Spaces Must be received by the 5th of the month. Gate Admission $20 First Space - includes $10 Cambridge Vendor License $15 Additional Spaces Admission is after the prepaid vendors Early Bird Buyer -Admission after the prepaid vendor line is admitted. ~ 7:15AM ** You may not sell. ** $15 per person at the gate. ****************************** cut here ******************************* FLEA at MIT 2005 Advance Space Application ____April ____May ____June ____ July ____Aug ___Sept ____Oct @ $17 for the first each month + $12 each additional Name ________________________ Call __________ $ Included______ Address ________________________ Phone __________ Make Check to The MIT Radio Society City ____________________ State _______ Zip _______ PO Box 397082 Cambridge MA 02139 E-mail _____________________________________________ ******************************************************************************* Steve Finberg W1GSL w1gsl@mit.edu PO Box 82 MIT Br Cambridge MA 02139-7082 617 258 3754 ******************************************************************************* Article: 93665 of rec.radio.amateur.homebrew From: "xpyttl" References: <6zvBe.1589$j21.575@news01.roc.ny> <11dd9ksc9hoeab5@corp.supernews.com> Subject: Re: What would cause the SWR to go up drastically when I turn my amp on? Message-ID: Date: Fri, 15 Jul 2005 16:27:57 -0400 "Roy Lewallen" wrote in message news:11dd9ksc9hoeab5@corp.supernews.com... > Joeseph wrote: > > , , , >> Assuming you are correct my next problem will stopping the extra >> frequencies from getting out of the amp in the first place. > > No, your problem should be figuring out how to prevent them from getting > generated in the first place. If the harmonic or spurious content is that > high, there's something seriously wrong. Nice answer, Roy. That was my knee-jerk, too. Joseph, remember, the problem isn't only "stopping them from getting out of the amp...". Those other frequencies are some sort of parasitic in the amplifier. Besides being stuff you don't want going to the antenna, they are robbing your amp of the ability to amplify the frequencies you DO want amplified, and they are unnecessarily heating up your transistors and sapping their life. So first, keep them from being generated, then stiffen up that low pass filter so anything that does get created is way, way down. Far lower than what will show up as an apparent SWR problem. .. Article: 93666 of rec.radio.amateur.homebrew From: "Pete KE9OA" References: Subject: Re: Murata Ceramic Filters Message-ID: Date: Fri, 15 Jul 2005 22:30:17 GMT Nice website you have there. The CFX455 filters have a center frequency of 455kHz, while the the CFX450 filters have a 455kHz center frequency. Pete "Derek Twynham" wrote in message news:db8bit$ebv$1@news.al.sw.ericsson.se... >> Does anyone know of a retail vendor that would sell the Murata ceramic >> filter CFJ455K5 without a $25-$5000 minimum order? > > http://www.barendh.com has: > > CFWM450I 4 12 455 Rather steep filter on 450kHz! > 9.90 > CFK455J 2.7 6 455 17x7 steil ssb > 36.50 > CFK455E 15 20 455 17x7 very steep > 19.90 > CFS455E 15 30 455 28x11 Steep filter > 32.50 > CFS455H 6 13 455 28x11 Steep filter > 32.50 > CFS455J 2.7 6 455 28x11 Steep filter > 35.00 > CFL455DG2 20 40 455 16x7 extremely flat group delay > 36.26 > CFR455G 12 22 455 7x22 Very steep > 19.95 > LFD15 15 25 455 28x11 Very steep > 44.92 > CFM455... several bandwidths stocked > CFM455H 6 15 455 ***STEEP- METAL CAN- SPEC.OFFER *** > 5.67 > CFM455A 35 70 455 7x22 Meteosat > 31.31 > CFG455F 12 25 455 7x11 Narrowband FM > 26.77 > CFG455I 4 9 455 7x11 Narrow AM > 29.00 > > (prices in Euros) > > Article: 93667 of rec.radio.amateur.homebrew From: mcalhoun@ksu.edu Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power supplies Date: 15 Jul 2005 17:51:36 -0500 Message-ID: References: <1121288717.540109.24910@g14g2000cwa.googlegroups.com> <1121399296.200297.165740@g44g2000cwa.googlegroups.com> <;-) Reminds me of another joke I can't quite remember: something >dealing with the proof that electricity is really smoke.... A local (and now retired) engineering faculty member has an after-dinner speech in which he "proves" that "electricity is black and heavy"! For example, in an automobile, electricity is stored in the battery. What color is the battery? Black! And it is quite heavy for its size. And on and on and on! --Myron. -- --Myron A. Calhoun. Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge PhD EE (retired). "Barbershop" tenor. CDL(PTXS). W0PBV. (785) 539-4448 NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol) Article: 93668 of rec.radio.amateur.homebrew From: Tim Wescott Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power supplies Date: Fri, 15 Jul 2005 16:51:21 -0700 Message-ID: <11dgivlmf1fhi32@corp.supernews.com> References: <1121288717.540109.24910@g14g2000cwa.googlegroups.com> <1121399296.200297.165740@g44g2000cwa.googlegroups.com> straydog wrote: > > > On Fri, 14 Jul 2005 LenAnderson@ieee.org wrote: > >> Date: 14 Jul 2005 20:48:16 -0700 >> From: LenAnderson@ieee.org >> Newsgroups: rec.radio.amateur.homebrew >> Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power >> supplies >> >> From: straydog on Fri 15 Jul 2005 00:48 >> >> >>> That's called trial and error. Or, try, smoke, fix. Like if ready, fire, >>> aim does not work, change the order to ready, aim, fire. >> >> >> All electronics works on smoke. If the smoke leaks out, >> it won't work... >> > > ;-) Reminds me of another joke I can't quite remember: something > dealing with the proof that electricity is really smoke, or something > like that. Maybe someone has a reference to that joke. It was pretty > funny, too. > > Art, W4PON > But electricity _is_ really smoke. They burn coal at the generating station and it travels through the wires to your house, where it makes everything work. Then the used smoke goes _back_ through the wires (why do you think they call them "return" wires, eh?) to the generating station where it goes up the smokestack. If something should break then some of the smoke will leak out right there in your house right before the thing stops working. And that's how you know that electricity is smoke. -- ------------------------------------------- Tim Wescott Wescott Design Services http://www.wescottdesign.com Article: 93669 of rec.radio.amateur.homebrew From: "RadioGuy" References: Subject: Re: Looking for 12V tube Rx project info Message-ID: Date: Sat, 16 Jul 2005 00:30:32 GMT Howdy: I got just what you are looking for... how about the 'WWII Prison Camp Short-wave Receiver' ? The circuit is claimed to be from, "United States Army in WWII The Technical Services, The Signal Corps: The Outcome, U.S. Government Printing Office, 1966." Check the circuit at: http://www.webex.net/~skywaves/SPY/spy.htm I collected parts but never had a chance to build it---old metal canteens are hard to find. RG ---------- Ed wrote in message news:Xns967D79AD24D7spectrumhogstarbandn@207.106.92.175... > > I am looking for a nice schematic, and perhaps additional info, on a 12V > (fil. & plate) tube superhet Rx; just something fairly simple for CW/SSB > reception without bells and whistles, and preferably for 75M/40M reception. > > Can anyone point me to info on this? Thanks. > > > > Ed K7AAT Article: 93670 of rec.radio.amateur.homebrew From: "RadioGuy" Subject: Finishing Aluminum Message-ID: Date: Sat, 16 Jul 2005 00:30:33 GMT Howdy: Its been a common practice with me to finish the aluminum surface of a chassis or box with an immersion into a caustic solution followed with a coating of clear acrylic spray---I like the satin finish it produces. I normally use lye that I regularly found on the shelves of our neighborhood hardware stores. However, I've been having a harder time of finding the flaked lye that I have used over the years for that purpose. I have used 'Lewis Red Devil Lye' that I found at Ace Hardware. A project that I am currently working on made me think of trying a substitute for lye with an item that I seem to find everywhere. Often found in the automotive stores is a product that is referred to as a 'cleaner/degreaser' or 'heavy duty industrial cleaner'. I have seen it marketed as 'Purple Stuff' yet I purchased a gallon called 'Right Stuff (Purple Stuff Concentrate)' manufactured by Sunbelt Chemicals, Palm Coast, Florida, 386.446.4595. Nevertheless, the contents of both bottles have a characteristic purple color and contains (besides sodium hydroxide) a component derived from citrus---but more importantly, the label states that the product is NOT TO BE USED ON ALUMINUM! I finished the surface of both halves of a mini-box by immersing them into a solution, by volume, of 1 part 'Right Stuff' to 8 parts warm water (I used 1:8 for no particular reason---It just happened that way). The surface of the aluminum began to bubble rapidly, but not uncontrollably, causing a fine white froth to appear on the surface of the solution. I let the mini-box soak for 30 minutes whereupon I removed them and placed them into a bucket of water. I found that the removal of the black residue is easier to achieve if I wash the aluminum parts while they remain under water---a sponge or cloth works fine and a Q-Tip removes the residue from corners. I observed that as the reaction proceeded the purple color of the solution became clear. Needless to say, I am entirely satisfied with the results. The dilute solution of 'Right Stuff' provided a uniform satin finish identical in appearance to a solution of lye (sodium hydroxide). If you can't find lye I suggest a solution of industrial cleaner possessing caustic properties. The next time I use 'Right Stuff' I will increase it by 1 part just to see the result. The reaction liberates hydrogen gas---use adequate ventilation. RG Article: 93671 of rec.radio.amateur.homebrew From: straydog Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power Date: Sat, 16 Jul 2005 00:57:56 +0000 Message-ID: References: <1121288717.540109.24910@g14g2000cwa.googlegroups.com> On Fri, 15 Jul 2005, Tim Wescott wrote: > Date: Fri, 15 Jul 2005 16:51:21 -0700 > From: Tim Wescott > Newsgroups: rec.radio.amateur.homebrew > Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power > supplies > > straydog wrote: > >> >> >> On Fri, 14 Jul 2005 LenAnderson@ieee.org wrote: >> >>> Date: 14 Jul 2005 20:48:16 -0700 >>> From: LenAnderson@ieee.org >>> Newsgroups: rec.radio.amateur.homebrew >>> Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power >>> supplies >>> >>> From: straydog on Fri 15 Jul 2005 00:48 >>> >>> >>>> That's called trial and error. Or, try, smoke, fix. Like if ready, fire, >>>> aim does not work, change the order to ready, aim, fire. >>> >>> >>> All electronics works on smoke. If the smoke leaks out, >>> it won't work... >>> >> >> ;-) Reminds me of another joke I can't quite remember: something >> dealing with the proof that electricity is really smoke, or something like >> that. Maybe someone has a reference to that joke. It was pretty funny, too. >> >> Art, W4PON >> > But electricity _is_ really smoke. They burn coal at the generating station > and it travels through the wires to your house, where it makes everything > work. Then the used smoke goes _back_ through the wires (why do you think > they call them "return" wires, eh?) to the generating station where it goes > up the smokestack. > > If something should break then some of the smoke will leak out right there in > your house right before the thing stops working. > > And that's how you know that electricity is smoke. That's pretty good, but I seem to recall another slightly different version of the joke but with some really clever line about the purpose of insulation (and a half-believable rationale [rationale does not mean scientific, however). Anyone else remember more of the details of this joke? Art, W4PON > -- > ------------------------------------------- > Tim Wescott > Wescott Design Services > http://www.wescottdesign.com > Article: 93672 of rec.radio.amateur.homebrew Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power supplies From: "Z.Z." References: <1121288717.540109.24910@g14g2000cwa.googlegroups.com> <1121399296.200297.165740@g44g2000cwa.googlegroups.com> Message-ID: Date: Sat, 16 Jul 2005 03:11:31 GMT Myron wrote: > > A local (and now retired) engineering faculty member has an after-dinner > speech in which he "proves" that "electricity is black and heavy"! > > For example, in an automobile, electricity is stored in the battery. > What color is the battery? Black! > And it is quite heavy for its size. > Sounds logical to me. My favoite is the Dark Sucker Theory (light is the absence of dark, and light bulds suck dark). Do a google on it for lots more info, probably more than you ever wanted to know... :-) And thusly another thread morphs far off topic... Article: 93673 of rec.radio.amateur.homebrew From: "Roger Conroy" Subject: Re: Finishing Aluminum Date: Sat, 16 Jul 2005 15:01:44 +0200 Message-ID: References: "RadioGuy" wrote in message news:JyYBe.425340$cg1.138579@bgtnsc04-news.ops.worldnet.att.net... > Howdy: > > Its been a common practice with me to finish the aluminum surface of a > chassis or box with an immersion into a caustic solution followed with a > coating of clear acrylic spray---I like the satin finish it produces. I > normally use lye that I regularly found on the shelves of our neighborhood > hardware stores. However, I've been having a harder time of finding the > flaked lye that I have used over the years for that purpose. I have used > 'Lewis Red Devil Lye' that I found at Ace Hardware. > > A project that I am currently working on made me think of trying a > substitute for lye with an item that I seem to find everywhere. Often > found > in the automotive stores is a product that is referred to as a > 'cleaner/degreaser' or 'heavy duty industrial cleaner'. I have seen it > marketed as 'Purple Stuff' yet I purchased a gallon called 'Right Stuff > (Purple Stuff Concentrate)' manufactured by Sunbelt Chemicals, Palm Coast, > Florida, 386.446.4595. Nevertheless, the contents of both bottles have a > characteristic purple color and contains (besides sodium hydroxide) a > component derived from citrus---but more importantly, the label states > that > the product is NOT TO BE USED ON ALUMINUM! > > I finished the surface of both halves of a mini-box by immersing them into > a > solution, by volume, of 1 part 'Right Stuff' to 8 parts warm water (I used > 1:8 for no particular reason---It just happened that way). The surface of > the aluminum began to bubble rapidly, but not uncontrollably, causing a > fine > white froth to appear on the surface of the solution. I let the mini-box > soak for 30 minutes whereupon I removed them and placed them into a bucket > of water. I found that the removal of the black residue is easier to > achieve if I wash the aluminum parts while they remain under water---a > sponge or cloth works fine and a Q-Tip removes the residue from corners. > I > observed that as the reaction proceeded the purple color of the solution > became clear. > > Needless to say, I am entirely satisfied with the results. The dilute > solution of 'Right Stuff' provided a uniform satin finish identical in > appearance to a solution of lye (sodium hydroxide). If you can't find lye > I > suggest a solution of industrial cleaner possessing caustic properties. > The > next time I use 'Right Stuff' I will increase it by 1 part just to see the > result. The reaction liberates hydrogen gas---use adequate ventilation. > > RG > > Has anyone ever tried mag wheel cleaner? It's specifically intende for use on Al/Mg Alloys. Article: 93674 of rec.radio.amateur.homebrew From: Gary S. Subject: Re: High Voltage Techniques Message-ID: <926id15f0f92rgq8s4li6q0c1eonesvpi0@4ax.com> References: <5fOdnQ8Hy6LPB0nfRVn-qw@giganews.com> <1121273199.297781.91510@g44g2000cwa.googlegroups.com> Date: Sat, 16 Jul 2005 14:34:38 GMT On Sat, 16 Jul 2005 02:31:49 -0500, "Ed" wrote: >Thanks all. Tom, I've been in electronics thirty years or so, but always >solid state.Now I'm going backwards to boatanchors. I know most of the old >sayings such as "keep one hand in your pocket" etc., but I'm more interested >in practical considerations of draining capacitors, proper wiring >techniques, and so forth. I know that even unplugged tube devices can jump >out and get you, and I'd like to avoid this...especially in high power RF >amplifiers. I've got Bill Orr's handbook, years of old magazines from the One thing to consider is to make and use a "chicken stick". Don't touch anything electrical until you have touched it with the chicken stick. This is essentially a ground wire (to a solid ground) with a well insulated handle. To avoid component damage, add a low ohmage, high wattage resistor in series. A chicken stick is routinely used in commercial HV equipment, and power company linemen have a portable equivalent. Better to be a live chicken than flambeed. Ref: Happy trails, Gary (net.yogi.bear) -- At the 51st percentile of ursine intelligence Gary D. Schwartz, Needham, MA, USA Please reply to: garyDOTschwartzATpoboxDOTcom Article: 93675 of rec.radio.amateur.homebrew From: "RadioGuy" References: Subject: Re: Finishing Aluminum Message-ID: <%LaCe.3098$5N3.2973@bgtnsc05-news.ops.worldnet.att.net> Date: Sat, 16 Jul 2005 16:40:27 GMT Wes Stewart wrote in message news:mc5id11o1ui9rn6d5ohsm6l81d4otgdrec@4ax.com... > On Sat, 16 Jul 2005 00:30:33 GMT, "RadioGuy" > wrote: > > >Howdy: > > > >Its been a common practice with me to finish the aluminum surface of a > >chassis or box with an immersion into a caustic solution followed with a > >coating of clear acrylic spray---I like the satin finish it produces. I > >normally use lye that I regularly found on the shelves of our neighborhood > >hardware stores. However, I've been having a harder time of finding the > >flaked lye that I have used over the years for that purpose. I have used > >'Lewis Red Devil Lye' that I found at Ace Hardware. > > I still have a couple of cans of Red Devil "in stock" after my last > project. That was the rejuvenation of a 20-year-old Yagi antenna. I > built a plastic sheet lined trough outside that was long enough to > hold the longest piece of tubing and had at it. I never thought of that for long pieces... thats a good tip. > >A project that I am currently working on made me think of trying a > >substitute for lye with an item that I seem to find everywhere. Often found > >in the automotive stores is a product that is referred to as a > >'cleaner/degreaser' or 'heavy duty industrial cleaner'. I have seen it > >marketed as 'Purple Stuff' yet I purchased a gallon called 'Right Stuff > >(Purple Stuff Concentrate)' manufactured by Sunbelt Chemicals, Palm Coast, > >Florida, 386.446.4595. Nevertheless, the contents of both bottles have a > >characteristic purple color and contains (besides sodium hydroxide) a > >component derived from citrus---but more importantly, the label states that > >the product is NOT TO BE USED ON ALUMINUM! > > > >I finished the surface of both halves of a mini-box by immersing them into a > >solution, by volume, of 1 part 'Right Stuff' to 8 parts warm water (I used > >1:8 for no particular reason---It just happened that way). The surface of > >the aluminum began to bubble rapidly, but not uncontrollably, causing a fine > >white froth to appear on the surface of the solution. I let the mini-box > >soak for 30 minutes whereupon I removed them and placed them into a bucket > >of water. I found that the removal of the black residue is easier to > >achieve if I wash the aluminum parts while they remain under water---a > >sponge or cloth works fine and a Q-Tip removes the residue from corners. I > >observed that as the reaction proceeded the purple color of the solution > >became clear. > > Good to know. You might find that a dip in vinegar will help with the > removal of the black smut. Thanks... I didn't know that! I often wondered if there was an easier way to remove the black residue. > >Needless to say, I am entirely satisfied with the results. The dilute > >solution of 'Right Stuff' provided a uniform satin finish identical in > >appearance to a solution of lye (sodium hydroxide). If you can't find lye I > >suggest a solution of industrial cleaner possessing caustic properties. The > >next time I use 'Right Stuff' I will increase it by 1 part just to see the > >result. The reaction liberates hydrogen gas---use adequate ventilation. > > If you want a really satiny surface, another trick I have used is to > sand the surface with an orbital sander and medium grit wet-dry paper > lubricated with light oil. It's a messy process but leaves an > interesting surface with the little "orbit" scratches and it's a good > way to recover badly scratched surfaces. Etching afterwards with lye > "softens" the effect and of coarse cleans the surface. I'll give that technique a try. Awhile back I heard that after the metal is finished in a lye bath then boiled in a solution of color dye (RIT) a colored, metallic finish, can be produced---one of these days I'll try it on a scrap piece. On simple projects I print or photocopy text then affix them onto to the aluminum surface (after a first coat of acrylic on the aluminum) with white glue then with multiple sprays of acrylic affix them permanently to the surface. It worked real nice with a bandpass filter project---I secured the graph of the filter characteristics onto the minibox for reference. RG Article: 93676 of rec.radio.amateur.homebrew From: inagaddadavida@webtv.net (Jim) Subject: build a variable capacitor Date: Sat, 16 Jul 2005 13:08:18 -0500 Message-ID: <6294-42D94D12-102@storefull-3255.bay.webtv.net> i need a variable for a receiving loop antenna. does anyone know how to determine the area of plates for a given value of cap? for example i need 365 pf. two half circle plates would be handy, separated by a piece of plastic or card stock. what surface area for each plate would approximate that value? does two stator plates with one rotor between them increase the value if compared to one plate each? Article: 93677 of rec.radio.amateur.homebrew From: inagaddadavida@webtv.net (Jim) Subject: Re: Unknown Component Date: Sat, 16 Jul 2005 13:35:08 -0500 Message-ID: <6295-42D9535C-23@storefull-3255.bay.webtv.net> References: i am not highly qualified as an electronics guy so maybe this is stupid, but isnt that a cap to reduce the spark as the contacts open? an old points ignition condenser is for that purpose and it is .02 mfd Article: 93678 of rec.radio.amateur.homebrew From: "Polymath" References: <6294-42D94D12-102@storefull-3255.bay.webtv.net> Subject: Re: build a variable capacitor Date: Sat, 16 Jul 2005 20:14:38 +0100 Message-ID: <42d95c5f$1_2@x-privat.org> for each facing pair, (ie with two fixed and one moving in between, you'll get two faces) C=eA/d e=permittivity of free space, A=area, d= separation. But you must use real scientific/engineering units, not those Yank Hillbilly ones. "Jim" wrote in message news:6294-42D94D12-102@storefull-3255.bay.webtv.net... >i need a variable for a receiving loop antenna. does anyone know how to > determine the area of plates for a given value of cap? for example i > need 365 pf. two half circle plates would be handy, separated by a piece > of plastic or card stock. what surface area for each plate would > approximate that value? does two stator plates with one rotor between > them increase the value if compared to one plate each? > Article: 93679 of rec.radio.amateur.homebrew From: dplatt@radagast.org (Dave Platt) Subject: Re: build a variable capacitor Date: Sat, 16 Jul 2005 19:23:30 -0000 Message-ID: <11dinli949oec23@corp.supernews.com> References: <6294-42D94D12-102@storefull-3255.bay.webtv.net> In article <6294-42D94D12-102@storefull-3255.bay.webtv.net>, Jim wrote: >i need a variable for a receiving loop antenna. does anyone know how to >determine the area of plates for a given value of cap? for example i >need 365 pf. two half circle plates would be handy, separated by a piece >of plastic or card stock. what surface area for each plate would >approximate that value? does two stator plates with one rotor between >them increase the value if compared to one plate each? For a parallel-plate capacitor, capacitance equals 0.0885 e[r] (N - 1) A / t where A is the area of one plate (in square inches), N is the number of plates, t is the thickness of the dielectric (separation between plates, in an air-variable cap) measured in inches, and e[r] is the dielectric constant of the dielectric (1.0 in the case of air). A cap with two stator plates and one rotor plate would have twice the capacitance of a cap with one stator and one rotor, all else being equal and neglecting parasitic effects. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! Article: 93680 of rec.radio.amateur.homebrew From: Gary S. Subject: Re: build a variable capacitor Message-ID: <4boid1huje51mv17v3lp1dc1jfb1dnnc61@4ax.com> References: <6294-42D94D12-102@storefull-3255.bay.webtv.net> Date: Sat, 16 Jul 2005 19:37:20 GMT On Sat, 16 Jul 2005 13:08:18 -0500, inagaddadavida@webtv.net (Jim) wrote: >i need a variable for a receiving loop antenna. does anyone know how to >determine the area of plates for a given value of cap? for example i >need 365 pf. two half circle plates would be handy, separated by a piece >of plastic or card stock. what surface area for each plate would >approximate that value? does two stator plates with one rotor between >them increase the value if compared to one plate each? The spacing between the plates is an important factor as well. You will need to construct it mechanically solid enough that the spacing does not change much. The dielectric material properties will have an effect as well, although smaller. Happy trails, Gary (net.yogi.bear) -- At the 51st percentile of ursine intelligence Gary D. Schwartz, Needham, MA, USA Please reply to: garyDOTschwartzATpoboxDOTcom Article: 93681 of rec.radio.amateur.homebrew From: dplatt@radagast.org (Dave Platt) Subject: Re: QUESTION: Cheap Accurate Shaft Position Encoder Date: Sat, 16 Jul 2005 23:44:06 -0000 Message-ID: <11dj6u6plpiab7b@corp.supernews.com> References: <1121290111.687842.193790@g49g2000cwa.googlegroups.com> <1121334811.401173.310790@g49g2000cwa.googlegroups.com> <1121556590.029730.3960@g14g2000cwa.googlegroups.com> In article <1121556590.029730.3960@g14g2000cwa.googlegroups.com>, >> I'm sure that limits stepper motors to certain uses, but I think this >> thread/post may be incorrectly titled. Unless I misunderstand the intended >> application, I don't think a "position encoder" is what he is looking for. >> Rather he wants something that, when rotated, feeds pulses to an up/down >> counter for frequency synthesis. The position of the shaft is not important >> as long as its rotation can be used to generate pulses for the counter. >> >> Roger > >Roger: > >Yes you're right, that's exactly what I'm looking for... any ideas as >to where I might get such a beast? Usually known as a "rotary encoder". They normally have two outputs, in a phase-quadrature arrangment. These can be decoded to create up/down/clock pulses using dedicated ICs (HP makes 'em), or via a small collection of discrete TTL logic chips, or via a simple software routine in a PIC micro or similar (which is how I'd probably do it these days... I wrote a simple state-table routine for an 8051 some years back which worked out quite well). You'll probably want at least 64 counts per revolution, and probably 256, to get a nice smooth "feel" to the synthesizer tuning. Most such use an optical code wheel and a pair of optosensors. Digi-Key catalog lists quite a few such (all with their own shafts, ready for panel mounting), but they aren't cheap. Mechanical rotary encoders are less expensive, but less precise (fewer counts per revolution) and possibly not as reliable or long-lived since they use mechanical contacts. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! Article: 93682 of rec.radio.amateur.homebrew From: Eamon Skelton Subject: Re: QUESTION: Cheap Accurate Shaft Position Encoder Message-ID: References: <1121290111.687842.193790@g49g2000cwa.googlegroups.com> <1PiBe.2051$_%4.856@newssvr14.news.prodigy.com> Date: Sun, 17 Jul 2005 01:54:34 +0000 On Thu, 14 Jul 2005 01:00:45 +0000, Roger Leone wrote: > Tim: > > There used to be a website with info on using surplus stepper motors as > precision shaft encoders. I have been doing Google searches without > success. Perhaps someone else will be able to provide a URL. It was > Australian, I believe. > > Good luck. > > Roger K6XQ That was probably on Richard Hosking's (VK6BRO) web-page. The page seems to have disappeared from the web. Hopefully it has moved to a new URL. Are you lurking here Richard? This page has some info: http://www.webx.dk/oz2cpu/20m/encoder.htm 73, Ed. EI9GQ. -- Linux 2.6.12.1 Remove 'X' to reply by e-mail. Article: 93683 of rec.radio.amateur.homebrew From: craigm Subject: Re: QUESTION: Cheap Accurate Shaft Position Encoder References: <1121290111.687842.193790@g49g2000cwa.googlegroups.com> <1PiBe.2051$_%4.856@newssvr14.news.prodigy.com> <1121334811.401173.310790@g49g2000cwa.googlegroups.com> <1121556590.029730.3960@g14g2000cwa.googlegroups.com> Message-ID: Date: Sat, 16 Jul 2005 20:29:17 -0500 Timothy@tholtom.freeserve.co.uk wrote: > > Roger Leone wrote: > >>>Steppers have no output unless the shaft is moving. Steppers used this >>>way are really a velocity encoder and not a position encoder. >>>Regards, >>>Glenn AC7ZN >>> >> >>Glenn: >> >>I'm sure that limits stepper motors to certain uses, but I think this >>thread/post may be incorrectly titled. Unless I misunderstand the intended >>application, I don't think a "position encoder" is what he is looking for. >>Rather he wants something that, when rotated, feeds pulses to an up/down >>counter for frequency synthesis. The position of the shaft is not important >>as long as its rotation can be used to generate pulses for the counter. >> >>Roger > > > Roger: > > Yes you're right, that's exactly what I'm looking for... any ideas as > to where I might get such a beast? > > Tim > For something inexpensive, consider the encoder in a wheel mouse. Also most ball mice include two encoders for the ball. craigm Article: 93684 of rec.radio.amateur.homebrew From: straydog Subject: Re: build a variable capacitor Date: Sun, 17 Jul 2005 01:58:56 +0000 Message-ID: References: <6294-42D94D12-102@storefull-3255.bay.webtv.net> On Sat, 16 Jul 2005, Jim wrote: > Date: Sat, 16 Jul 2005 13:08:18 -0500 > From: Jim > Newsgroups: rec.radio.amateur.homebrew > Subject: build a variable capacitor > > i need a variable for a receiving loop antenna. does anyone know how to > determine the area of plates for a given value of cap? for example i > need 365 pf. two half circle plates would be handy, separated by a piece > of plastic or card stock. what surface area for each plate would > approximate that value? does two stator plates with one rotor between > them increase the value if compared to one plate each? > > Do you really need to build this? I know they (365 mfd variables) are hard to find (I'd love to find a cheap source, expensive sources on the internet want $10-15 each [google on "365 mfd" to find them]), but if you go to a thrift store (Salvation Army, etc.), you may find old transistor clock radios for $1-2 each that have miniature 365 mfd variables that will do just fine if you take a few minutes to de-solder them from the circuit board. Art, W4PON Article: 93685 of rec.radio.amateur.homebrew From: "xpyttl" References: <1121290111.687842.193790@g49g2000cwa.googlegroups.com> <1121334811.401173.310790@g49g2000cwa.googlegroups.com> <1121556590.029730.3960@g14g2000cwa.googlegroups.com> <11dj6u6plpiab7b@corp.supernews.com> Subject: Re: QUESTION: Cheap Accurate Shaft Position Encoder Message-ID: Date: Sat, 16 Jul 2005 22:24:24 -0400 "Dave Platt" wrote in message news:11dj6u6plpiab7b@corp.supernews.com... > In article <1121556590.029730.3960@g14g2000cwa.googlegroups.com>, > Digi-Key catalog lists quite a few such (all with their own shafts, > ready for panel mounting), but they aren't cheap. Mechanical rotary > encoders are less expensive, but less precise (fewer counts per > revolution) and possibly not as reliable or long-lived since they use > mechanical contacts. Depending on the application, mechanical encoders are pretty good, and getting better. As a tuning control, in most cases something on the order of 50 pulses per rev is pretty useable and avaliable in a mechanical encoder. Much more than that and you are getting into the optical encoders which do get kind of pricey. They -feel- really nice, though. Most of the mechanical encoders Digikey carries are detented, so watch out for that. The few that aren't are pretty decent. Mechanical encoders are typically under $5, while the opticals are more like $50. But the nice ball-bearing feel might be worth it, depending on your project. .. Article: 93686 of rec.radio.amateur.homebrew From: mcalhoun@ksu.edu Subject: Re: QUESTION: Fun with Svetlanas or Staying alive with kV power supplies Date: 17 Jul 2005 05:51:16 -0500 Message-ID: References: <1121288717.540109.24910@g14g2000cwa.googlegroups.com> <1121399296.200297.165740@g44g2000cwa.googlegroups.com> <11dgivlmf1fhi32@corp.supernews.com> >But electricity _is_ really smoke. They burn coal at the generating >station and it travels through the wires to your house, where it makes .... Did you notice that coal is BLACK? And most smoke is BLACK, too. Insofar as water-generated electricity is concerned, it comes from rain which has FALLEN (it's heavy) out of BLACK clouds and flowed downward (heavy, again) to a sort of centrifuge which spins the HEAVY electricity out of the water and forces it into the wires.... -- --Myron A. Calhoun. Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge PhD EE (retired). "Barbershop" tenor. CDL(PTXS). W0PBV. (785) 539-4448 NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol) Article: 93687 of rec.radio.amateur.homebrew From: mcalhoun@ksu.edu Subject: Re: build a variable capacitor Date: 17 Jul 2005 06:03:11 -0500 Message-ID: References: <6294-42D94D12-102@storefull-3255.bay.webtv.net> <3NadnfAtAehA-ETfRVnytQ@pipex.net> >>i need a variable for a receiving loop antenna.... >In the May 2005 issue of 'Electron' ( mag of VERON ,the IARU affiliated >society in the Netherlands) there is an article , by PE1LKT ,on a homebrew >'sliding 'capacitor made of pieces of double sided printed circuit board. >5 plates are fixed with 4 plates sliding in between..... QST has published several homemade-capacitors articles in the last few years: * A Home-Brew Loop Tuning Capacitor (November, 1994) * A Homemade High-Power Tuning Capacitor (June, 1983) * One I recall (but can't find; my QST's are paper, someone with the QST CDs could do a search) which used concentric tubes with thin plastic around the inner/inside the outer Ok, so "few" is relative at my age!-) -- --Myron A. Calhoun. Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge PhD EE (retired). "Barbershop" tenor. CDL(PTXS). W0PBV. (785) 539-4448 NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol) Article: 93688 of rec.radio.amateur.homebrew From: "Polymath" References: <6294-42D94D12-102@storefull-3255.bay.webtv.net> <42DA3D21.4080306@bloomer.net> Subject: Re: build a variable capacitor Date: Sun, 17 Jul 2005 12:18:48 +0100 Message-ID: <42da3e51$1_2@x-privat.org> "Manufacture" = "Make By Hand" "Scott" wrote in message news:42DA3D21.4080306@bloomer.net... > Of course, you CAN build the capacitor, but unless you want to do it for > fun and/or education, why re-invent the wheel? Dan's Small Parts and Kits > sells several nice capacitors. > > http://www.danssmallpartsandkits.net/ > > The capacitors aren't necessarily "dirt cheap", but a manufactured > capacitor will be physically stable, insuring smooth change in capacitance > as the shaft is rotated. > > Scott > N0EDV > > Jim wrote: >> i need a variable for a receiving loop antenna. does anyone know how to >> determine the area of plates for a given value of cap? for example i >> need 365 pf. two half circle plates would be handy, separated by a piece >> of plastic or card stock. what surface area for each plate would >> approximate that value? does two stator plates with one rotor between >> them increase the value if compared to one plate each? >> Article: 93689 of rec.radio.amateur.homebrew From: Cliff Subject: Is there affordable software I can use to map out circuit traces for a printed circuit board? Message-ID: Date: Sun, 17 Jul 2005 13:53:50 GMT I about ready to design and build my own solid state RF amp. Is there a good and affordable piece of software out there that I can use to neatly map out the circuit traces for my printed circuit board. Article: 93690 of rec.radio.amateur.homebrew Date: Sun, 17 Jul 2005 10:16:52 -0400 From: -ex- Subject: Re: Finishing Aluminum References: <%LaCe.3098$5N3.2973@bgtnsc05-news.ops.worldnet.att.net> <5dokd1hq1vqimmh0vm8qntl6bq1dgvoptl@4ax.com> Message-ID: <92d74$42da6856$4232bd57$23078@COQUI.NET> Wes Stewart wrote: > On Sat, 16 Jul 2005 16:40:27 GMT, "RadioGuy" > >>On simple projects I print or photocopy text then affix them onto to the >>aluminum surface (after a first coat of acrylic on the aluminum) with white >>glue then with multiple sprays of acrylic affix them permanently to the >>surface. It worked real nice with a bandpass filter project---I secured the >>graph of the filter characteristics onto the minibox for reference. > > > Nice idea. I use the ruboff lettering (Datak) but of course they > don't have any BPF response curves, [g] > On a bare metal panel the homebrew inkjet waterslide decals work quite well and you could do your response curve with that method. -Bill Article: 93691 of rec.radio.amateur.homebrew From: dplatt@radagast.org (Dave Platt) Subject: Re: Is there affordable software I can use to map out circuit traces for a printed circuit board? Date: Sun, 17 Jul 2005 16:38:54 -0000 Message-ID: <11dl2cu479tle6f@corp.supernews.com> References: > I about ready to design and build my own solid state RF amp. Is >there a good and affordable piece of software out there that I can use >to neatly map out the circuit traces for my printed circuit board. http://www.cadsoft.de/freeware.htm might be sufficient, depending on the size of the board you plan to make. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! Article: 93692 of rec.radio.amateur.homebrew From: dplatt@radagast.org (Dave Platt) Subject: Re: Finishing Aluminum Date: Sun, 17 Jul 2005 16:46:44 -0000 Message-ID: <11dl2rkm6qgvlbe@corp.supernews.com> References: <%LaCe.3098$5N3.2973@bgtnsc05-news.ops.worldnet.att.net> <5dokd1hq1vqimmh0vm8qntl6bq1dgvoptl@4ax.com> In article <5dokd1hq1vqimmh0vm8qntl6bq1dgvoptl@4ax.com>, Wes Stewart wrote: >>> Good to know. You might find that a dip in vinegar will help with the >>> removal of the black smut. >> >>Thanks... I didn't know that! I often wondered if there was an easier way >>to remove the black residue. > >Actually, a stronger acid works better (quicker). The "blackness" >seems to depend on the alloy and it may still take light rubbing to >get the stubborn stuff off. As I understand it, the black stuff is usually referred to as "smut". It's the other metals in the alloy, left behind when the lye dissolves the aluminum. Anodizing shops will follow the lye-etch with a plunge into a "bright dip" acid bath to de-smut the surface and leave it nice and shiny. Bright dip mixtures seem to vary - one I've seen mentioned is mostly phosphoric acid, with a few percent of nitric acid added. Kinda nasty stuff. >>Awhile back I heard that after the metal is finished in a lye bath then >>boiled in a solution of color dye (RIT) a colored, metallic finish, can be >>produced---one of these days I'll try it on a scrap piece. > >Now you're starting into anodizing. See: > >http://w3.uwyo.edu/~metal/anodizing.html Yup. A common cycle seems to be: drill and sand, etch in lye, bright-dip to de-smut, anodize to build up a porous layer of hard aluminum oxide, boil in dye to color, seal. One problem with the use of RIT color dyes is that they aren't all that stable against UV, and can fade over time. There are professional anodizing dyes which are more stable. >>On simple projects I print or photocopy text then affix them onto to the >>aluminum surface (after a first coat of acrylic on the aluminum) with white >>glue then with multiple sprays of acrylic affix them permanently to the >>surface. It worked real nice with a bandpass filter project---I secured the >>graph of the filter characteristics onto the minibox for reference. > >Nice idea. I use the ruboff lettering (Datak) but of course they >don't have any BPF response curves, [g] The Brother plastic-laminated labelling tapes seem to work fairly well, also. I usually use the standard black-text-on-white-background and then spray with acrylic. The black-on-clear might look nice on an aluminum case, but I haven't tries this myself yet. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! Article: 93693 of rec.radio.amateur.homebrew From: "Reg Edwards" Subject: Resistor frequency response Date: Sun, 17 Jul 2005 17:15:42 +0000 (UTC) Message-ID: FREQUENCY RESPONSE OF RESISTORS. Program METALFLM.exe 41 Kbytes. This program models small low-wattage wire-ended resistors including spiralled metal-film resistors. The model's equivalent circuit is a chain of T and L networks. Values of lumped inductance and stray capacitance are estimated by the program from the component's physical dimensions. The component with it's terminating leads is treated as a lumped L and C non-uniform transmission line. The program computes input impedance >from 10 KHz up to 5 GHz with the other end grounded. Fast and slow frequency sweeps are available to observe maxima and minima of Zin. Max and min Zin are approximately related to the physical length of the component, including connecting leads, but occur at frequencies far higher than the usual and useful working frequency range. The reflection cefficient and standing-wave-ratio are calculated with reference to Zo, Zo being the DC value of the resistor. The usefulness of the component as a dummy load or for other purposes at any frequency can then be ascertained. The effectiveness versus frequency of solid carbon-rod resistors and multi-turn UHF chokes, which are of similar wire-end construction, can also be determined. Chokes can be wound over the bodies of high-value wire-ended resistors, the parallel resistance value perhaps having some desirable effect on the ultimate response. Another use for resistors having a good high frequency response, or at least a known frequency response, is for ratio arms and switched resistors in impedance bridges and other measuring instruments. Download METALFLM in a few seconds and run immediately. ---- ........................................................... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp ........................................................... Article: 93694 of rec.radio.amateur.homebrew From: Win Subject: Re: Unknown Component Date: Sun, 17 Jul 2005 12:43:42 -0500 Message-ID: References: <6295-42D9535C-23@storefull-3255.bay.webtv.net> On Sat, 16 Jul 2005 13:35:08 -0500, inagaddadavida@webtv.net (Jim) wrote: >i am not highly qualified as an electronics guy so maybe this is stupid, >but isnt that a cap to reduce the spark as the contacts open? an old >points ignition condenser is for that purpose and it is .02 mfd Maybe you are more qualified than youy think. Yes, it is a MilSpec cap, probably for that exact purpose. Win, W0LZl Article: 93695 of rec.radio.amateur.homebrew From: crusty@REMOVE_THIS_lsmo.sytes.net Subject: Re: Is there affordable software I can use to map out circuit traces for a printed circuit board? Message-ID: References: Date: Sun, 17 Jul 2005 17:56:09 GMT EasyTrax is a freeware program Protel released for DOS computers years ago. it will run on Windows 98 in a DOS windowm too. Do a google search and you'll find many sites that have it for download. One note, it doesn't have surface mount pads, so it's through-hole or kludge in the SM parts. On Sun, 17 Jul 2005 13:53:50 GMT, Cliff wrote: > > I about ready to design and build my own solid state RF amp. Is >there a good and affordable piece of software out there that I can use >to neatly map out the circuit traces for my printed circuit board. > Article: 93696 of rec.radio.amateur.homebrew Subject: Silver Mica vs Mica Caps From: "Z.Z." Message-ID: Date: Sun, 17 Jul 2005 18:22:54 GMT What's the difference between a silver mica cap and a plain old mica cap? Is there any? I mean with respect to size, performance, stability, voltage ratings, etc. Where would one be used instead of the other? Thanks... Article: 93697 of rec.radio.amateur.homebrew From: "Henry Kolesnik" References: Subject: Re: Silver Mica vs Mica Caps Message-ID: Date: Sun, 17 Jul 2005 18:36:30 GMT Silver micas cost more and had a better spec for capacitance, temperature as well as aging and are used in circuits where you want to minimize frequency drift. IIRC silver was plated somehow onto the higher grade mica whereas ordinary micas used a lower grade o f mica and weren't plated or plated as well. -- 73 Hank WD5JFR "Z.Z." wrote in message news:Xns969673C8813E3nobodynowhere@68.6.19.6... > What's the difference between a silver mica cap and a plain old mica cap? > Is there any? I mean with respect to size, performance, stability, voltage > ratings, etc. Where would one be used instead of the other? > > Thanks... Article: 93698 of rec.radio.amateur.homebrew From: "Mario Bros" Subject: TCXO Clipped Sine Wave Message-ID: Date: Sun, 17 Jul 2005 20:34:25 GMT Hi folks, I would have to ask a clarification regard to the TCXO. They are found with output TTL, HCMOS and CLIPPED SINE WAVE. It is just with respect to this last type that I would want to have elucidations on when it is convenient to employ it, which the advantages and the disadvantages and which the extension of spectral harmonicas. In synthesis, from the plan point of view, which are the motivations that they make to incline towards a Clipped oscillator? Anticipated thanks. 73's de IK6GQC Rocco Article: 93699 of rec.radio.amateur.homebrew From: "xpyttl" References: <1121290111.687842.193790@g49g2000cwa.googlegroups.com> <1121334811.401173.310790@g49g2000cwa.googlegroups.com> <1121556590.029730.3960@g14g2000cwa.googlegroups.com> <11dj6u6plpiab7b@corp.supernews.com> Subject: Re: QUESTION: Cheap Accurate Shaft Position Encoder Message-ID: <8uACe.17$xR1.2@fe04.lga> Date: Sun, 17 Jul 2005 17:56:14 -0400 "Ian White G/GM3SEK" wrote in message news:PxxDykEjBh2CFAB1@ifwtech.co.uk... > For something like a receiver tuning control, even 256 steps/rev would > sound 'jumpy'. However, you could gear it up mechanically so that even a Actually, 256 is getting too high in most cases. The "jumpiness" comes from the size of the step, i.e., the number of Hz per step. Encoders between 50 and 100 are probably the easiest to deal with. You generally want to make the step size small, like 1 or 10 Hz, but you don't want hundreds of turns to cover the band. At very high resolutions, the pulses can come very fast, so it gets tricky to distinguish the closure from noise. Of course, higher counts can be made to work, and in principle, can be made to work better. But generally, one is dealing with low level software and finite compute resources to read the encoder, so the very high resolutions can actually become somewhat problematic. .. Article: 93700 of rec.radio.amateur.homebrew From: crusty@REMOVE_THIS_lsmo.sytes.net Subject: Re: TCXO Clipped Sine Wave Message-ID: <5jlld1pi35n5hpsb5o6nqfkhq69uv48opq@4ax.com> References: Date: Sun, 17 Jul 2005 22:12:56 GMT The clipped sinewave is the simplest output for a TCXO, it's usually just a capacitor connected between the emitter of the oscillator and the output pin. You have to be careful what you connect to it, it's possible to throw the temp compensation out of tolerance. Most CMOS PLL chips have a reference frequency input that handles it well. If you're rolling your own PLL from SSI or MSI chips, you probable want to build up a buffer to make the clipped sinewave into TTL or HCMOS levels, or pay extra for a TCXO with the needed circuit built in. On Sun, 17 Jul 2005 20:34:25 GMT, "Mario Bros" wrote: >Hi folks, >I would have to ask a clarification regard to the TCXO. >They are found with output TTL, HCMOS and CLIPPED SINE WAVE. >It is just with respect to this last type that I would want to have >elucidations on when it is convenient to employ it, which the advantages and >the disadvantages and which the extension of spectral harmonicas. >In synthesis, from the plan point of view, which are the motivations that >they make to incline towards a Clipped oscillator? > >Anticipated thanks. > >73's de IK6GQC Rocco > Article: 93701 of rec.radio.amateur.homebrew Date: Sun, 17 Jul 2005 20:10:06 -0400 From: -ex- Subject: Re: Simple questions on receivers References: <1121199166.494373.59190@g49g2000cwa.googlegroups.com> <1121402521.763416.59680@z14g2000cwz.googlegroups.com> <3ab17$42d74ce4$4232bd6a$15556@COQUI.NET> <1121640125.959490.41200@g47g2000cwa.googlegroups.com> Message-ID: <50c4f$42daf364$4232bd1b$8913@COQUI.NET> dave.harper wrote: > > -ex- wrote: > >>Q in excess of 1000 is readily achievable. 200-300 is a starting point >>on a decent dx set. > > > So what's a good inductance to DC resistance ratio for an inductor on > an xtal set? The one I wound is about 500uH, and I get a resistance of > 3.2 Ohms. > > Using the formula Q=2*pi*f*L/R, I get a Q for my coil of 981 (@1MHz). > But based on its performance, I KNOW it's not that good. I'm picking > up a couple stations at night, but just barely. > > Dave For BCB work the 'standard' is in the 220-240uh range for tuning with a ~365-400 pf cap. There's an (almost) infinite number of combinations you can use if you want to split the band into segments which sometimes has an advantage. But switches and tapped coils can also be Q-killers once you get into the Q stratosphere. In practice the coil Q is determined primarily by the form dielectric, wire size, wire spacing, diameter/length ratio/neary coupling effects, etc. R is far enough down the list that its generally not even considered. When you do a DC measurement of coil R thats not representative of the skin effects and true RF resistance, thats why the textbook formula doesn't pan out. If you want to make a fairly nice coil without getting into the expense of litz, check out spider-web coils and rook coils. When done with say 16-18 ga wire, and diameters in the 4" range you can get a pretty nice coil. With 166-strand litz (30-35c/ft) you'll note an improvement but by that time its time to start thinking about a good hi-q ceramic capacitor and circuit loading concerns. The Rap-n-Tap forum is where to get some good info. http://www.midnightscience.com/rapntap/ "Best coil" is a common topic! -Bill Article: 93702 of rec.radio.amateur.homebrew Message-ID: <42DB2344.656CF54E@pcbguys.com> From: pcb_dude Subject: Re: Is there affordable software I can use to map out circuit traces for References: Date: Mon, 18 Jul 2005 03:34:30 GMT http://www.expresspcb.com/ Cliff wrote: > I about ready to design and build my own solid state RF amp. Is > there a good and affordable piece of software out there that I can use > to neatly map out the circuit traces for my printed circuit board. Article: 93703 of rec.radio.amateur.homebrew From: Jim Adney Subject: Re: Silver Mica vs Mica Caps Date: Sun, 17 Jul 2005 23:18:42 -0500 Message-ID: References: On Sun, 17 Jul 2005 18:22:54 GMT "Z.Z." wrote: >What's the difference between a silver mica cap and a plain old mica cap? >Is there any? I mean with respect to size, performance, stability, voltage >ratings, etc. Where would one be used instead of the other? I believe these are just 2 different names for the same thing. Silver mica caps come in various cases, and those cases have varied over the decades, but they've always consisted of a mica wafer plated on each side. I've never seen a manufacturer's catalog that made this distinction. The little mica compression variables would be an exception, as those are not plated, but I suspect you're not asking about those. - ----------------------------------------------- Jim Adney jadney@vwtype3.org Madison, WI 53711 USA ----------------------------------------------- Article: 93704 of rec.radio.amateur.homebrew Date: Mon, 18 Jul 2005 01:03:27 -0400 From: -ex- Subject: Re: Simple questions on receivers References: <1121199166.494373.59190@g49g2000cwa.googlegroups.com> <1121402521.763416.59680@z14g2000cwz.googlegroups.com> <3ab17$42d74ce4$4232bd6a$15556@COQUI.NET> <1121640125.959490.41200@g47g2000cwa.googlegroups.com> <1121645911.200886.19170@g43g2000cwa.googlegroups.com> Message-ID: <1eca0$42db3823$4232be43$19553@COQUI.NET> LenAnderson@ieee.org wrote: > Q alone won't determine sensitivity. Very true. In fact the opposite is usually the case when it comes to function. In a good hi-q xtal set one often has to sacrifice sensitivity for selectivity...and vice-versa. Tighter coupling=more sensitivity but less selectivity because of loading effects. If you want sensitivity, go outdoors and hang wire or add sound-powered headphones. If you want selectivity, tweak the ckt. But still, by aiming for highest Q you at least have something to work with when trading off. Crystal radios are somewhat like a house of mirrors. Changes at one end reflect at the other end of the ckt. The old razor-blade radio is an example of everything being done the worst way but it still works. As you improve on the scheme each component becomes more and more critical. -Bill Article: 93705 of rec.radio.amateur.homebrew Date: Mon, 18 Jul 2005 01:15:24 -0400 From: -ex- Subject: Re: Silver Mica vs Mica Caps References: Message-ID: <23000$42db3af0$4232be43$20080@COQUI.NET> Jim Adney wrote: > >>What's the difference between a silver mica cap and a plain old mica cap? >>Is there any? I mean with respect to size, performance, stability, voltage >>ratings, etc. Where would one be used instead of the other? > > > I believe these are just 2 different names for the same thing. Silver > mica caps come in various cases, and those cases have varied over the > decades, but they've always consisted of a mica wafer plated on each > side. > > I've never seen a manufacturer's catalog that made this distinction. Oh, no. Not at all true. Before about say 1940, mica caps were truly a sandwich of simple alternating metal plates and mica insulators. About 1950-ish they began 'plating' the mica. Silvering is a mixed blessing. Many of the original silvered-mica caps now exhibit migration (leakage) problems. It doesn't go without noting that in the 50s mica caps were not at all en vogue. Precision caps went thru an era where the ceramic (silvered) dogbone style were the most common. Nowadays, I'm not sure exactly what it is I'm buying when I buy the "dipped mica" caps. I'm confident to say they are better than the old-timers but are they silver plated onto mica or what? -Bill Article: 93706 of rec.radio.amateur.homebrew From: "Mario Bros" References: <5jlld1pi35n5hpsb5o6nqfkhq69uv48opq@4ax.com> Subject: Re: TCXO Clipped Sine Wave Message-ID: Date: Mon, 18 Jul 2005 11:26:24 GMT Thanks for the answers. I have one TCXO 40Mhz 1Vp-p 10K//15pf Clipped Sine Wave. My idea is of: 1) to gain 40Mhz Sine Wave through buffer with resonant circuit come to an agreement for 2nd the IF (40.455) 2) to gain 20Mhz with a divisor x2 for the 16F877 3) ..and last.. to gain before 120Mhz (40x3) and then 480Mhz with helical filter for clock the AD9954. Thoughts are possible? It is one bad solutions?? Thank you again. ha scritto nel messaggio news:5jlld1pi35n5hpsb5o6nqfkhq69uv48opq@4ax.com... > The clipped sinewave is the simplest output for a TCXO, it's usually just > a > capacitor connected between the emitter of the oscillator and the output > pin. > You have to be careful what you connect to it, it's possible to throw the > temp > compensation out of tolerance. Most CMOS PLL chips have a reference > frequency > input that handles it well. If you're rolling your own PLL from SSI or MSI > chips, you probable want to build up a buffer to make the clipped sinewave > into > TTL or HCMOS levels, or pay extra for a TCXO with the needed circuit built > in. > > > > > On Sun, 17 Jul 2005 20:34:25 GMT, "Mario Bros" wrote: > >>Hi folks, >>I would have to ask a clarification regard to the TCXO. >>They are found with output TTL, HCMOS and CLIPPED SINE WAVE. >>It is just with respect to this last type that I would want to have >>elucidations on when it is convenient to employ it, which the advantages >>and >>the disadvantages and which the extension of spectral harmonicas. >>In synthesis, from the plan point of view, which are the motivations that >>they make to incline towards a Clipped oscillator? >> >>Anticipated thanks. >> >>73's de IK6GQC Rocco >> > Article: 93707 of rec.radio.amateur.homebrew From: straydog Subject: Re: Silver Mica vs Mica Caps Date: Mon, 18 Jul 2005 13:39:05 +0000 Message-ID: References: On Sun, 17 Jul 2005, Z.Z. wrote: > Date: Sun, 17 Jul 2005 18:22:54 GMT > From: Z.Z. > Newsgroups: rec.radio.amateur.homebrew > Subject: Silver Mica vs Mica Caps > > What's the difference between a silver mica cap and a plain old mica cap? > Is there any? I mean with respect to size, performance, stability, voltage > ratings, etc. Where would one be used instead of the other? > > Thanks... > Yes, there is a difference and catalogs should say "silver mica" and if they don't then they are not silver mica. Today's sales people may not be techie literate and so today's catalogs may be less accurate. Silver micas were a little more expensive, too. Besides a higher price, the overall performance specs were better besides haveing lower losses and better accuracy. Most of the time, silver micas were meant for free-running VFO circuits (IIRC) because you wanted thermal stability and as little losses to lead to heat which would cause drift. However, if you wanted to be clever, you would get a set of negative temperature coefficient capacitors and use them to balance out the (all the rest of them) positive temperature coefficient capacitors and thus arive at a very low warm-up drift free running VFO. I'm from the old days. Today, its all phase-locked-loop VFOs and "throw away" rigs when they break (nobody fixes stuff anymore [pardon my exageration]). Art, W4PON Article: 93708 of rec.radio.amateur.homebrew From: "Heriberto" References: Subject: Re: Murata Ceramic Filters Date: Mon, 18 Jul 2005 12:38:36 -0300 Message-ID: <42dbca7e_1@x-privat.org> What is the diference? Tito LU6DBU "Pete KE9OA" escribió en el mensaje news:ZNWBe.424884$cg1.303128@bgtnsc04-news.ops.worldnet.att.net... > Nice website you have there. The CFX455 filters have a center frequency of > 455kHz, while the the CFX450 filters have a 455kHz center frequency. > > Pete > > "Derek Twynham" wrote in message > news:db8bit$ebv$1@news.al.sw.ericsson.se... > >> Does anyone know of a retail vendor that would sell the Murata ceramic > >> filter CFJ455K5 without a $25-$5000 minimum order? > > > > http://www.barendh.com has: > > > > CFWM450I 4 12 455 Rather steep filter on 450kHz! > > 9.90 > > CFK455J 2.7 6 455 17x7 steil ssb > > 36.50 > > CFK455E 15 20 455 17x7 very steep > > 19.90 > > CFS455E 15 30 455 28x11 Steep filter > > 32.50 > > CFS455H 6 13 455 28x11 Steep filter > > 32.50 > > CFS455J 2.7 6 455 28x11 Steep filter > > 35.00 > > CFL455DG2 20 40 455 16x7 extremely flat group delay > > 36.26 > > CFR455G 12 22 455 7x22 Very steep > > 19.95 > > LFD15 15 25 455 28x11 Very steep > > 44.92 > > CFM455... several bandwidths stocked > > CFM455H 6 15 455 ***STEEP- METAL CAN- SPEC.OFFER *** > > 5.67 > > CFM455A 35 70 455 7x22 Meteosat > > 31.31 > > CFG455F 12 25 455 7x11 Narrowband FM > > 26.77 > > CFG455I 4 9 455 7x11 Narrow AM > > 29.00 > > > > (prices in Euros) > > > > > > Article: 93709 of rec.radio.amateur.homebrew From: straydog Subject: Re: Simple questions on receivers Date: Mon, 18 Jul 2005 21:51:54 +0000 Message-ID: References: <1121199166.494373.59190@g49g2000cwa.googlegroups.com> On Mon, 18 Jul 2005, dave.harper wrote: > Date: 18 Jul 2005 14:18:03 -0700 > From: dave.harper > Newsgroups: rec.radio.amateur.homebrew, rec.radio.amateur.misc > Subject: Re: Simple questions on receivers > > -ex- wrote: > >> I've had good success with ferrite toroids approaching Q=400, although >> ferrites are by nature very unpredictable Q-wise. > > Is this the reason a lot of coils are air coils? 1. Air core coils will be cheaper, lighter in weight, easier to make. > Easy of calculations? 2. Definitely. > I assume you can get higher performance from ferrite coils than > air-core coils, right? You don't need as much ampere-turns to get a given amount of inductance and thus, ohmic resistance will be less, therefore higher Q (in theory). caveat: the magnetizable material you use for the core (i.e. iron, ferrite, and other stuff that I think other guys here surely know better than I) will have a big effect on useable frequency on up to some cut-off threshold that may be sharp or spread out. Pure solid sheet iron, for example, might be good at audio frequencies and maybe up to x00,000 Hertz, but you need powdered iron to go into the megacycle range. There are other core substances that get you up higher. Anyone else care to add to this? Don't forget that winding a torroidal coil is not so easy. Some cores are available in halves so you can make "pies", otherwise the "bobbin" carrying the wire has to pass through the hole of the doughnut many times. > Thanks again! > Dave > > Art, W4PON Article: 93710 of rec.radio.amateur.homebrew Date: Mon, 18 Jul 2005 18:10:45 -0400 From: -ex- Subject: Re: Simple questions on receivers References: <1121199166.494373.59190@g49g2000cwa.googlegroups.com> <11d8bpfoa35o6c3@corp.supernews.com> <1121392518.226007.109060@g44g2000cwa.googlegroups.com> <6ff44$42d7220c$4232bd6a$2073@COQUI.NET> <1121721483.202961.268810@z14g2000cwz.googlegroups.com> Message-ID: <5a033$42dc28e9$4232bda1$6814@COQUI.NET> My comments are interspersed. -Bill straydog wrote: > > > On Mon, 18 Jul 2005, dave.harper wrote: >> >> Is this the reason a lot of coils are air coils? > > > 1. Air core coils will be cheaper, lighter in weight, easier to make. A typical medium-sized ferrite toroid coil for BCB use, FT-82-61 for instance, costs about US$1 and can't weigh more than an ounce and uses up about 4-5 feet of wire. > >> Easy of calculations? > > > 2. Definitely. Different calculation but one is as easy as the other. Just look for an online calculator :) > iron, for example, might be good at audio frequencies and maybe up to > x00,000 Hertz, but you need powdered iron to go into the megacycle > range. There are other core substances that get you up higher. Anyone > else care to add to this? True. There are two main substances used in ferrite toroids - and I can't quote either name - and they have vastly different permeability characteristics. I think the CWS-Bytemark website goes into some of these details. > Don't forget that winding a torroidal coil is not so easy. Some cores > are available in halves so you can make "pies", otherwise the "bobbin" > carrying the wire has to pass through the hole of the doughnut many times. I've been referring to the simple doughnut cores. A BCB coil takes around 50 turns on -61 material. Even with my fat fingers it only takes about 10 minutes. -Bill Article: 93711 of rec.radio.amateur.homebrew From: Larry Gagnon Subject: Re: Finishing Aluminum Date: Mon, 18 Jul 2005 16:22:29 -0700 Message-ID: References: On Sat, 16 Jul 2005 00:30:33 +0000, RadioGuy wrote: > Howdy: > > Its been a common practice with me to finish the aluminum surface of a > chassis or box with an immersion into a caustic solution followed with a > coating of clear acrylic spray---I like the satin finish it produces. I > normally use lye that I regularly found on the shelves of our neighborhood > hardware stores. However, I've been having a harder time of finding the > flaked lye that I have used over the years for that purpose. I have used > 'Lewis Red Devil Lye' that I found at Ace Hardware. [snip] Am I correct in understanding that TSP, also called Sugar Soap (the stuff used by many to wash walls before painting) is essentially mostly lye? If so that is quite a cheap source you might want to consider. Larry VE7EA Article: 93712 of rec.radio.amateur.homebrew From: dplatt@radagast.org (Dave Platt) Subject: Re: Finishing Aluminum Date: Mon, 18 Jul 2005 23:36:33 -0000 Message-ID: <11dof81dvap8mcb@corp.supernews.com> References: In article , Larry Gagnon wrote: >Am I correct in understanding that TSP, also called Sugar Soap (the stuff >used by many to wash walls before painting) is essentially mostly lye? Nope. TSP is Tri-sodium phosphate. "TSP substitute" is apparently often composed largely of sodium carbonate ("washing soda" or "soda ash"). I believe that both of these chemicals will attack aluminum, but that the reactions are a lot slower than is the case with lye (sodium hydroxide). -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! Article: 93713 of rec.radio.amateur.homebrew From: "Mike Andrews" Subject: Re: Finishing Aluminum Date: Tue, 19 Jul 2005 00:05:59 +0000 (UTC) Message-ID: References: Larry Gagnon wrote: > On Sat, 16 Jul 2005 00:30:33 +0000, RadioGuy wrote: >> Howdy: >> >> Its been a common practice with me to finish the aluminum surface of a >> chassis or box with an immersion into a caustic solution followed with a >> coating of clear acrylic spray---I like the satin finish it produces. I >> normally use lye that I regularly found on the shelves of our neighborhood >> hardware stores. However, I've been having a harder time of finding the >> flaked lye that I have used over the years for that purpose. I have used >> 'Lewis Red Devil Lye' that I found at Ace Hardware. > [snip] > Am I correct in understanding that TSP, also called Sugar Soap (the stuff > used by many to wash walls before painting) is essentially mostly lye? If > so that is quite a cheap source you might want to consider. TSP is Tri-Sodium Phosphate; lye is Sodium Hydroxide. They're different compounds with different properties. Sodium Hydroxide is incredibly nasty if mishandled: the human body does not handle strong bases well, and Sodium Hydroxide eats flesh with terrible avidity. It's really, really easy to lose meat or an eye to a drop or three in the wrong place. I wear long gloves, a plastic apron, a long-sleeved shirt, goggles _and_ a face shield whenever I have to work with it. TSP, while much less nasty, is still nothing to play with. Google for the Material Safety Datasheets (MSDS) on both. -- Before long, Microsoft will attempt to patent the alphabet (hoping we'll have to pay royalties to use our keyboards and keep their stock solid). -- Phil Paxton Article: 93714 of rec.radio.amateur.homebrew From: mcalhoun@ksu.edu Subject: Re: Finishing Aluminum Date: 18 Jul 2005 21:34:00 -0500 Message-ID: References: <11dof81dvap8mcb@corp.supernews.com> >>Am I correct in understanding that TSP, also called Sugar Soap.... >Nope. TSP is Tri-sodium phosphate... So what is in Draino? -- --Myron A. Calhoun. Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge PhD EE (retired). "Barbershop" tenor. CDL(PTXS). W0PBV. (785) 539-4448 NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol) Article: 93715 of rec.radio.amateur.homebrew From: "Mario Bros" References: <5jlld1pi35n5hpsb5o6nqfkhq69uv48opq@4ax.com> <1121749815.727527.170530@o13g2000cwo.googlegroups.com> Subject: Re: TCXO Clipped Sine Wave Message-ID: Date: Tue, 19 Jul 2005 10:32:44 GMT Hi Tom, Thanks for the councils. An alternative could be an oscillator (480 Mhz) with 1/4 coax resonator and IC PLL TSA5511 I2C Bus clocked by 40Mhz/10 (4mhz)... I must think to us... Ciao IK6GQC Rocco "K7ITM" ha scritto nel messaggio news:1121749815.727527.170530@o13g2000cwo.googlegroups.com... > It all sounds possible to me. It is not very different from some of > the schemes we use commercially to generate internal frequencies (in > spectral analysis equipment). Your idea of good filtering at 480MHz > (and also, I hope, at 120MHz) is a good one, to keep out other > combinations of multiplication. The one other thing I would be careful > about is the phase noise of the oscillator. The AD9954 should be > capable of very good phase noise performance, but you MUST feed it a > clean reference to keep the output clean. I have recently tested some > TCXOs which are very stable and accurate, but whose phase noise is not > as good as I would really like. It is important to feed the oscillator > from a very clean supply, but that alone is not a guarantee of good > phase noise. See http://www.techlib.com/electronics/finesse.html for a > nice idea to make a very clean supply for circuits that draw > essentially constant current. > > Cheers, > Tom > Article: 93716 of rec.radio.amateur.homebrew From: Jim Higgins Subject: Re: Finishing Aluminum Message-ID: References: Date: Tue, 19 Jul 2005 14:20:34 GMT On Mon, 18 Jul 2005 16:22:29 -0700, in , Larry Gagnon wrote: >On Sat, 16 Jul 2005 00:30:33 +0000, RadioGuy wrote: > >> Howdy: >> >> Its been a common practice with me to finish the aluminum surface of a >> chassis or box with an immersion into a caustic solution followed with a >> coating of clear acrylic spray---I like the satin finish it produces. I >> normally use lye that I regularly found on the shelves of our neighborhood >> hardware stores. However, I've been having a harder time of finding the >> flaked lye that I have used over the years for that purpose. I have used >> 'Lewis Red Devil Lye' that I found at Ace Hardware. >[snip] > >Am I correct in understanding that TSP, also called Sugar Soap (the stuff >used by many to wash walls before painting) is essentially mostly lye? If >so that is quite a cheap source you might want to consider. TSP is Tri-sodium phosphate. It forms an alkaline solution when dissolved in water, but it isn't as harsh as lye. It's meant to achieve the same result as lye via the alkaline solution it forms, but without as much danger to the user.